Wireless communication method for simultaneous data communication, and wireless communication terminal using same

ABSTRACT

For this, provided are a wireless communication method and a wireless communication terminal using the same. The method includes: receiving a wireless signal of a specific channel; extracting basic service set (BSS) identifier information of the received wireless signal; extracting length information from the wireless signal wherein the length information represents information relating to a transmission completion time point of the wireless signal; and adjusting a data transmission period of the terminal based on the extracted length information, when the BSS identifier information of the wireless signal is different from BSS identifier information of the terminal.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.15/674,501 filed on Aug. 10, 2017, which is a continuation of U.S.patent application Ser. No. 15/435,261 filed on Feb. 16, 2017, which isa continuation of International Patent Application No. PCT/KR2015/008498filed on Aug. 13, 2015, which claims the priority to Korean PatentApplication No. 10-2014-0107321 filed in the Korean IntellectualProperty Office on Aug. 18, 2014, Korean Patent Application No.10-2014-0170812 filed in the Korean Intellectual Property Office on Dec.2, 2014, and Korean Patent Application No. 10-2015-0035308 filed in theKorean Intellectual Property Office on Mar. 13, 2015, the entirecontents of which are incorporated herein by reference.

TECHNICAL FIELD

The present invention relates to a wireless communication method forsimultaneous data communication and a wireless communication terminalusing the same, and more particularly, to a wireless communicationmethod for suppressing interference between terminals and ensuringfairness when performing simultaneous data communication for spatialreuse of communication system and wireless communication terminal usingthe same.

BACKGROUND ART

In recent years, with supply expansion of mobile apparatuses, a wirelessLAN technology that can provide a rapid wireless Internet service to themobile apparatuses has been significantly spotlighted. The wireless LANtechnology allows mobile apparatuses including a smart phone, a smartpad, a laptop computer, a portable multimedia player, an embeddedapparatus, and the like to wirelessly access the Internet in home or acompany or a specific service providing area based on a wirelesscommunication technology in a short range.

Institute of Electrical and Electronics Engineers (IEEE) 802.11 hascommercialized or developed various technological standards since aninitial wireless LAN technology is supported using frequencies of 2.4GHz. First, the IEEE 802.1b supports a communication speed of a maximumof 11 Mbps while using frequencies of a 2.4 GHz band. IEEE 802.11a whichis commercialized after the IEEE 802.11b uses frequencies of not the 2.4GHz band but a 5 GHz band to reduce an influence by interference ascompared with the frequencies of the 2.4 GHz band which aresignificantly congested and improves the communication speed up to amaximum of 54 Mbps by using an OFDM technology. However, the IEEE802.11a has a disadvantage in that a communication distance is shorterthan the IEEE 802.11b. In addition, IEEE 802.11g uses the frequencies ofthe 2.4 GHz band similarly to the IEEE 802.11b to implement thecommunication speed of a maximum of 54 Mbps and satisfies backwardcompatibility to significantly come into the spotlight and further, issuperior to the IEEE 802.11a in terms of the communication distance.

Moreover, as a technology standard established to overcome a limitationof the communication speed which is pointed out as a weak point in awireless LAN, IEEE 802.11n has been provided. The IEEE 802.11n aims atincreasing the speed and reliability of a network and extending anoperating distance of a wireless network. In more detail, the IEEE802.11n supports a high throughput (HT) in which a data processing speedis a maximum of 540 Mbps or more and further, is based on a multipleinputs and multiple outputs (MIMO) technology in which multiple antennasare used at both sides of a transmitting unit and a receiving unit inorder to minimize a transmission error and optimize a data speed.Further, the standard can use a coding scheme that transmits multiplecopies which overlap with each other in order to increase datareliability.

As the supply of the wireless LAN is activated and further, applicationsusing the wireless LAN are diversified, the need for new wireless LANsystems for supporting a higher throughput (very high throughput (VHT))than the data processing speed supported by the IEEE 802.11n has comeinto the spotlight. Among them, IEEE 802.11ac supports a wide bandwidth(80 to 160 MHz) in the 5 GHz frequencies. The IEEE 802.11ac standard isdefined only in the 5 GHz band, but initial 11ac chipsets will supporteven operations in the 2.4 GHz band for the backward compatibility withthe existing 2.4 GHz band products. Theoretically, according to thestandard, wireless LAN speeds of multiple stations are enabled up to aminimum of 1 Gbps and a maximum single link speed is enabled up to aminimum of 500 Mbps. This is achieved by extending concepts of a radiointerface accepted by 802.11n, such as a wider radio frequency bandwidth(a maximum of 160 MHz), more MIMO spatial streams (a maximum of 8),multi-user MIMO, and high-density modulation (a maximum of 256 QAM).Further, as a scheme that transmits data by using a 60 GHz band insteadof the existing 2.4 GHz/5 GHz, IEEE 802.11ad has been provided. The IEEE802.11ad is a transmission standard that provides a speed of a maximumof 7 Gbps by using a beamforming technology and is suitable for high bitrate moving picture streaming such as massive data or non-compression HDvideo. However, since it is difficult for the 60 GHz frequency band topass through an obstacle, it is disadvantageous in that the 60 GHzfrequency band can be used only among devices in a short-distance space.

Meanwhile, in recent years, as next-generation wireless LAN standardsafter the 802.11ac and 802.11ad, discussion for providing ahigh-efficiency and high-performance wireless LAN communicationtechnology in a high-density environment is continuously performed. Thatis, in a next-generation wireless LAN environment, communication havinghigh frequency efficiency needs to be provided indoors/outdoors underthe presence of high-density stations and access points (APs) andvarious technologies for implementing the communication are required.

DISCLOSURE Technical Problem

As described above, an object of the present invention is to providehigh-efficiency/high-performance wireless LAN communication in ahigh-density environment.

In particular, an object of the present invention is to provide a methodfor efficiently transmitting data in an overlapped basic service set(BSS) environment.

Further, another object of the present invention is to increase atransmission opportunity and transmission rate of data by providing anefficient spatial reuse method in the overlapped BSS environment.

Further, another object of the present invention is to eliminate theunfairness problem of a legacy terminal that may occur when an adjustedCCA threshold is used for channel access.

Further, another object of the present invention is to minimize aninterference problem between terminals in a spatial reuse period.

Technical Solution

In order to achieve the objects, the present invention provides awireless communication method and a wireless communication terminal asbelow.

First, the present invention provides a wireless communication method ofa terminal including: receiving a wireless signal of a specific channel;measuring a signal strength of the received wireless signal; anddetermining whether the specific channel is busy based on the measuredsignal strength and BSS identifier information of the wireless signal.

In this case, the determining may be performed based on clear channelassessment (CCA) for the specific channel, and a CCA threshold used forthe CCA may be set to different levels according to whether the BSSidentifier information of the wireless signal is the same as BSSidentifier information of the terminal.

Further, when the BSS identifier information of the wireless signal isthe same as BSS identifier information of the terminal, a first CCAthreshold may be used for the CCA and when the BSS identifierinformation of the wireless signal is different from BSS identifierinformation of the terminal, a second CCA threshold having a higherlevel than the first CCA threshold may be used for the CCA.

In addition, the wireless communication method may further includeobtaining at least one of legacy wireless LAN information and non-legacywireless LAN information by using preamble information of the receivedwireless signal, wherein in the determining, when the non-legacywireless LAN information is obtained from the wireless signal, whetherthe specific channel is busy may be determined based on the BSSidentifier information of the wireless signal.

Next, the present invention provides a wireless communication method ofa terminal including: receiving a wireless signal of a specific channel;measuring a signal strength of the received wireless signal; obtainingat least one of legacy wireless LAN information and non-legacy wirelessLAN information by using preamble information of the received wirelesssignal; and determining whether the specific channel is busy based onBSS identifier information of the wireless signal when the measuredsignal strength is between a first clear channel assessment (CCA)threshold and a second CCA threshold and the non-legacy wireless LANinformation is obtained from the wireless signal.

In this case, the BSS identifier information of the wireless signal mayrepresent abbreviated information of a BSS identifier for the wirelesssignal.

According to the embodiment of the present invention, in thedetermining, whether the specific channel is busy may be determinedbased on a result of comparing the BSS identifier information of thewireless signal and the BSS identifier information of the terminal.

In this case, in the determining, when the BSS identifier information ofthe wireless signal is different from the BSS identifier information ofthe terminal, it may be determined that the specific channel is in anidle state.

Further, in the determining, when the BSS identifier information of thewireless signal is the same as the BSS identifier information of theterminal, it may be determined that the specific channel is in a busystate.

According to an embodiment of the present invention, the wireless signalmay include a first preamble for a legacy terminal and a second preamblefor a non-legacy terminal, and the BSS identifier information of thewireless signal may be extracted from the second preamble of thewireless signal.

According to another embodiment of the present invention, the wirelesssignal may be configured to include the first preamble for the legacyterminal and the second preamble for the non-legacy terminal and thefirst preamble may be configured to at least include a first subcarrierset for the legacy terminal, and when the first preamble is configuredto additionally include a second subcarrier set different from the firstsubcarrier set, the non-legacy wireless LAN information may be obtainedfrom the second subcarrier set.

In this case, the BSS identifier information of the received wirelesssignal may be extracted from information on the second subcarrier set ofthe first preamble.

According to yet another embodiment of the present invention, thewireless signal may include the first preamble for the legacy terminaland the second preamble for the non-legacy terminal, and whether thewireless signal includes the non-legacy wireless LAN information isdetermined based on information on predetermined bits of the firstpreamble.

According to an embodiment of the present invention, the wireless signalmay include the first preamble for the legacy terminal and the secondpreamble for the non-legacy terminal, and the BSS identifier informationof the wireless signal may be extracted from the predetermined bit fieldof the first preamble.

In this case, a predetermined bit of the predetermined bit field mayrepresent whether the wireless signal includes the non-legacy wirelessLAN information, and when the predetermined bit represents that thewireless signal includes the non-legacy wireless LAN information, theBSS identifier information of the wireless signal may be extracted fromthe predetermined bit field.

According to another embodiment of the present invention, the firstpreamble may be configured to at least include the first subcarrier setfor the legacy terminal, and when the first preamble is configured toadditionally include the second subcarrier set different from the firstsubcarrier set, the BSS identifier information of the wireless signalmay be extracted from the predetermined bit field.

Next, the present invention provides a wireless communication method ofa terminal including: receiving a wireless signal of a specific channel;extracting basic service set (BSS) identifier information of thereceived wireless signal; extracting length information from thewireless signal wherein the length information represents informationrelating to a transmission completion time point of the wireless signal;and adjusting a data transmission period of the terminal based on theextracted length information, when the BSS identifier information of thewireless signal is different from BSS identifier information of theterminal.

According to an embodiment, the length information representsinformation of a duration field in a frame of the wireless signal.

According to another embodiment, the length information representstransmission opportunity (TXOP) of an external terminal transmitting thewireless signal.

In this case, the length information is information obtained from atleast one of a legacy preamble, a non-legacy preamble, and a MAC headerof the wireless signal.

According to an embodiment of the present invention, the datatransmission period is adjusted to be terminated before the transmissioncompletion time point of the wireless signal according to the extractedlength information.

More specifically, the data transmission period is adjusted to beterminated before the transmission completion time point of the wirelesssignal by more than a sum value of a short inter frame space (SIFS) timeand a time required for transmission of a response message.

Additionally, the data transmission period represents a transmissionopportunity (TXOP) of the terminal.

According to a further embodiment of the present invention, the methodfurther includes: measuring a signal strength of the wireless signal;and determining whether the specific channel is busy based on themeasured signal strength and the extracted BSS identifier information,wherein the data transmission period is adjusted when the specificchannel is determined to be in an idle state and the terminal accessesthe specific channel.

Additionally, the determining of whether the specific channel is busy isperformed based on Clear Channel Assessment (CCA) for the specificchannel, and a CCA threshold used for the CCA is set to different levelsaccording to whether the BBS identifier information of the wirelesssignal is the same as the BSS identifier information of the terminal.

In this case, when the BBS identifier information of the wireless signalis the same as the BSS identifier information of the terminal, the firstCCA threshold is used for the CCA and when the BBS identifierinformation of the wireless signal is different from the BSS identifierinformation of the terminal, a second CCA threshold having a higherlevel than the first CCA threshold is used for the CCA.

Next, the present invention provides a wireless communication methodincluding: receiving a wireless signal of a specific channel; performinga clear channel assessment (CCA) based on a second CCA threshold whichis higher than a first CCA threshold for a legacy terminal if thewireless signal has BSS identifier information different from aterminal; performing a backoff procedure when the channel is determinedto be in an idle state as a result of the CCA; adjusting a backoffcounter assigned to the terminal if the backoff procedure is suspendedbefore the backoff counter of the backoff procedure expires; andresuming the backoff procedure using the adjusted backoff counter if thechannel is in an idle state again.

In this case, the backoff counter assigned to the terminal is adjustedwhen the received signal strength of the wireless signal during theperforming of the backoff procedure is between the first CCA thresholdand the second CCA threshold.

According to an embodiment, the adjusting of the backoff counterrestores the backoff counter to a value prior to the backoff procedure.

According to another embodiment, the adjusting of the backoff procedureallocates a new backoff counter for the terminal.

Next, the present invention provides a wireless communication method ofa terminal including: being assigned a first backoff counter and asecond backoff counter for a backoff procedure of the terminal;receiving a wireless signal having BSS identifier information differentfrom that of the terminal; performing a backoff procedure based on thereceived signal strength of the wireless signal, wherein the backoffprocedure consumes the first backoff counter when the received signalstrength of the wireless signal is lower than a first clear channelassessment (CCA) threshold for a legacy terminal, and wherein thebackoff procedure consumes the second backoff counter when the receivedsignal strength of the wireless signal is higher than the first CCAthreshold and lower than the second CCA threshold; and transmitting datawhen at least one of the first backoff counter and the second backoffcounter expires.

According to an embodiment of the present invention, the first backoffcounter and the second backoff counter are assigned in different randomnumber ranges.

Next, the present invention provides a wireless communication method ofa terminal including: receiving a request message (other BSS requestmessage) having BSS identifier information different from that of theterminal; receiving a response message (other BSS response message)corresponding to the other BSS request message; and determining whetherthe terminal accesses the channel based on a received signal strength ofthe other BSS request message and a received signal strength of theother BSS response message.

According to an embodiment of the present invention, when the receivedsignal strength of the other BSS response message is lower than thefirst CCA threshold and the received signal strength of the other BSSrequest message is lower than the second CCA threshold, the access ofthe terminal is allowed, wherein the second CCA threshold is set to ahigher level than the first CCA threshold.

According to a further embodiment of the present invention, the methodfurther includes, when it is determined that the terminal accesses thechannel, transmitting a request message (same BSS request message) to areception terminal indicating that data transmission of the terminal ispossible; and transmitting data to the reception terminal when a sameBSS response message corresponding to the same BSS request message isreceived from the reception terminal.

In this case, if the same BSS response message corresponding to the sameBSS request message is not received from the reception terminal, theterminal defers channel access.

According to an embodiment, the request message is a request-to-send(RTS) message, and the response message is a clear-to-send (CTS)message.

According to another embodiment, the request message is null data packet(NDP), and the response message is ACK.

According to another embodiment, the request message is MAC protocoldata unit (MPDU), and the response message is ACK.

Next, the present invention provides a wireless communication method ofa terminal including: receiving a request message (other BSS requestmessage) having BSS identifier information different from the terminal;receiving a response message (other BSS response message) correspondingto the other BSS request message; receiving from a transmission terminala request message (same BSS request message) which has the same BSSidentifier information as the terminal and uses the terminal as areceiver; and determining whether to transmit a same BSS responsemessage corresponding to the same BSS request message based on thereceived signal strength of the other BSS request message and thereceived signal strength of the other BSS response message.

In this case, the same BSS response message indicates that data of thetransmission terminal can be received.

According to an embodiment of the present invention, when the receivedsignal strength of the other BSS response message is lower than thefirst CCA threshold and the received signal strength of the other BSSrequest message is lower than the second CCA threshold, the same BSSresponse message is transmitted to the transmission terminal, but thesecond CCA threshold is set to a higher level than the first CCAthreshold.

According to an embodiment, the request message is a request-to-send(RTS) message, and the response message is a clear-to-send (CTS)message.

According to another embodiment, the request message is null data packet(NDP), and the response message is ACK.

According to another embodiment, the request message is MAC protocoldata unit (MPDU), and the response message is ACK.

Next, the present invention provides a wireless communication terminalincluding: a transceiver transmitting and receiving a wireless signal;and a processor controlling an operation of the terminal, wherein theprocessor measures a signal strength of a wireless signal of a specificchannel, which is received through the transceiver, and determineswhether the specific channel is busy based on the measured signalstrength and BSS identifier information of the wireless signal.

In this case, the processor may obtain at least one of legacy wirelessLAN information and non-legacy wireless LAN information by usingpreamble information of the received wireless signal, and determine,when the non-legacy wireless LAN information is obtained from thewireless signal, whether the specific channel is busy based on the BSSidentifier information of the wireless signal.

Further, the processor may perform the determination based on clearchannel assessment (CCA) for the specific channel, and a CCA thresholdused for the CCA may be set to different levels according to whether theBSS identifier information of the wireless signal is the same as BSSidentifier information of the terminal.

Next, the present invention provides a wireless communication terminalincluding: a transceiver transmitting and receiving a wireless signal;and a processor controlling an operation of the terminal, wherein theprocessor measures a signal strength of the wireless signal receivedthrough the transceiver; obtains at least one of legacy wireless LANinformation and non-legacy wireless LAN information by using preambleinformation of the received wireless signal; and determines whether thespecific channel is busy based on BSS identifier information of thewireless signal when the measured signal strength is between a firstclear channel assessment (CCA) threshold and a second CCA threshold andthe non-legacy wireless LAN information is obtained from the wirelesssignal.

Next, the present invention provides a wireless communication terminalincluding: a transceiver for transmitting and receiving a wirelesssignal; and a processor for controlling an operation of the terminalwherein the terminal receives a wireless signal of a specific channelthrough the transceiver, and wherein the processor extracts BSSidentifier information of the received wireless signal, extracts lengthinformation from the wireless signal the length information representinginformation related to the transmission completion time point of thewireless signal, and adjusts the data transmission period of theterminal based on the extracted length information, when the BSSidentifier information of the wireless signal is different from BSSidentifier information of the terminal.

Next, the present invention provides a wireless communication terminalincluding: a transceiver for transmitting and receiving a wirelesssignal; and a processor for controlling an operation of the terminalwherein the terminal receives a wireless signal of a specific channel,and wherein the processor performs a clear channel assessment (CCA)based on a second CCA threshold higher than a first CCA threshold for alegacy terminal if the wireless signal has BSS identifier informationdifferent from a terminal; performs a backoff procedure when the channelis determined to be in an idle state as a result of the CCA; adjusts abackoff counter assigned to the terminal if the backoff procedure issuspended before the backoff counter of the backoff procedure expires;and resumes the backoff procedure using the adjusted backoff counter ifthe channel is in an idle state again.

Next, the present invention provides a wireless communication terminalincluding: a transceiver for transmitting and receiving a wirelesssignal; and a processor for controlling an operation of the terminalwherein the terminal receives a wireless signal having BSS identifierinformation different from the terminal through the transceiver, andwherein the processor is assigned a first backoff counter and a secondbackoff counter for the backoff procedure of the terminal, performs abackoff procedure based on the received signal strength of the wirelesssignal, the backoff procedure consuming the first backoff counter whenthe received signal strength of the wireless signal is lower than afirst clear channel assessment (CCA) threshold for a legacy terminal,and the backoff procedure consuming the second backoff counter when thereceived signal strength of the wireless signal is higher than the firstCCA threshold and lower than a second CCA threshold, and transmits datawhen at least one of the first backoff counter and the second backoffcounter expires.

Next, the present invention provides a wireless communication terminalincluding: a transceiver for transmitting and receiving a wirelesssignal; and a processor for controlling an operation of the terminal,wherein the terminal receives a request message (other BSS requestmessage) having BSS identifier information different from that of theterminal through the transceiver and receives a response message (otherBSS response message) corresponding to the other BSS request message,and wherein the processor determines whether the terminal accesses thechannel based on a received signal strength of the other BSS requestmessage and a received signal strength of the other BSS responsemessage.

Next, the present invention provides a wireless communication terminalincluding: a transceiver for transmitting and receiving a wirelesssignal; and a processor for controlling an operation of the terminal,wherein the terminal receives a request message (other BSS requestmessage) having BSS identifier information different from the terminal,receives a response message (other BSS response message) correspondingto the other BSS request message, and receives from a transmissionterminal a request message (same BSS request message) which has the sameBSS identifier information as the terminal and uses the terminal as areceiver, and wherein the processor determines whether to transmit asame BSS response message corresponding to the same BSS request messagebased on the received signal strength of the other BSS request messageand the received signal strength of the other BSS response message.

Advantageous Effects

According to embodiments of the present invention, it can be efficientlydetermined whether a wireless signal received in an overlapped BSSenvironment is a wireless LAN signal of the same BSS and whether toadaptively use the corresponding channel can be decided based on thedetermination.

Further, according to another embodiment of the present invention, whenthe received wireless signal is a legacy wireless LAN signal from whichBSS identifier information is not extracted, whether the channel is in abusy state is determined according to a received signal strength of thecorresponding signal in a lump to minimize a time delay required toadditionally determine a BSS identifier of the legacy wireless LANsignal during a CCA process.

Further, according to another embodiment of the present invention, whena wireless LAN signal having the same BSS identifier information as thatof a terminal is received, an inequity problem in which different CCAthresholds are applied according to whether the corresponding wirelessLAN signal includes non-legacy wireless LAN information can be resolved.That is, CCA thresholds for a legacy signal and a non-legacy signal aresimilarly applied to the wireless LAN signal having the same BSSidentifier information as that of the terminal to maintain equity forchannel occupation between a legacy terminal and a non-legacy terminal.

According to yet another embodiment of the present invention, since atleast some of non-legacy wireless LAN information such as the BSSidentifier information can be obtained from a legacy preamble beforechecking a non-legacy preamble, CCA may be performed within a shortertime.

According to still another embodiment of the present invention, whendata transmission is performed in the spatial reuse period of anon-legacy terminal, the data transmission period of a correspondingterminal may be adjusted based on length information extracted from areceived wireless signal, and through this, it is possible to solve thechannel access delay problem of a legacy terminal.

Also, according to an embodiment of the present invention, mutualinterference may be minimized effectively while a plurality of terminalsperform communication at the same time.

DESCRIPTION OF DRAWINGS

FIG. 1 is a diagram illustrating a wireless LAN system according to anembodiment of the present invention.

FIG. 2 is a diagram illustrating a wireless LAN system according toanother embodiment of the present invention.

FIG. 3 is a block diagram illustrating a configuration of a stationaccording to an embodiment of the present invention.

FIG. 4 is a block diagram illustrating a configuration of an accesspoint according to an embodiment of the present invention.

FIG. 5 is a diagram illustrating a carrier sense multiple access(CSMA)/collision avoidance (CA) method used in wireless LANcommunication.

FIG. 6 is a diagram illustrating one embodiment of a wirelesscommunication scheme using a CCA technique.

FIG. 7 is a diagram illustrating one example of an overlapped BSSenvironment.

FIGS. 8 to 10 are diagrams illustrating various embodiments of a CCAmethod using BSS identifier information of a received wireless signal.

FIGS. 11 to 13 are diagrams illustrating another embodiment of a CCAmethod using whether to obtain non-legacy wireless LAN information froma received wireless signal and BSS identifier information.

FIG. 14 is a diagram illustrating a frame structure of a wireless LANsignal according to an embodiment of the present invention.

FIG. 15 is a diagram illustrating a method for representing BSSidentifier information according to an embodiment of the presentinvention.

FIG. 16 is a diagram illustrating an embodiment of a subcarrierconfiguration used in a legacy preamble of a wireless LAN signal.

FIG. 17 is a diagram illustrating an embodiment of a subcarrierconfiguration used in a non-legacy wireless LAN signal.

FIG. 18 is a diagram illustrating a method for representing non-legacywireless LAN information by using a predetermined bit field of thelegacy preamble.

FIG. 19 is a diagram illustrating the unfairness problem of a legacyterminal that may occur if an adjusted CCA threshold is used for channelaccess according to an embodiment of the present invention.

FIGS. 20 to 23 are diagrams illustrating the data transmission method ofa non-legacy terminal for solving the channel access delay problem of alegacy terminal.

FIG. 24 is a diagram illustrating another embodiment of the presentinvention to solve the unfairness problem of a legacy terminal that mayoccur if an adjusted CCA threshold is used for channel access.

FIG. 25 is a diagram illustrating an interference problem that may occurif an adjusted CCA threshold is used for channel access according to anembodiment of the present invention.

FIGS. 26 to 27 are diagrams illustrating the data transmission method ofa non-legacy terminal for minimizing an interference problem betweenterminals.

FIGS. 28 and 29 are diagrams illustrating another interference problemthat may occur if an adjusted CCA threshold is used for channel accessaccording to an embodiment of the present invention.

FIG. 30 is a diagram illustrating the data transmission method of anon-legacy terminal for minimizing an interference problem betweenterminals according to another embodiment of the present invention.

BEST MODE

Terms used in the specification adopt general terms which are currentlywidely used by considering functions in the present invention, but theterms may be changed depending on an intention of those skilled in theart, customs, and emergence of new technology. Further, in a specificcase, there is a term arbitrarily selected by an applicant and in thiscase, a meaning thereof will be described in a corresponding descriptionpart of the invention. Accordingly, it should be revealed that a termused in the specification should be analyzed based on not just a name ofthe term but a substantial meaning of the term and contents throughoutthe specification.

Throughout this specification and the claims that follow, when it isdescribed that an element is “coupled” to another element, the elementmay be “directly coupled” to the other element or “electrically coupled”to the other element through a third element. Further, unless explicitlydescribed to the contrary, the word “comprise” and variations such as“comprises” or “comprising”, will be understood to imply the inclusionof stated elements but not the exclusion of any other elements.Moreover, limitations such as “or more” or “or less” based on a specificthreshold may be appropriately substituted with “more than” or “lessthan”, respectively.

This application claims priority to and the benefit of Korean PatentApplication Nos. 10-2014-0107321, 10-2014-0170812, and 10-2015-0035308filed in the Korean Intellectual Property Office and the embodiments andmentioned items described in the respective applications are included inthe Detailed Description of the present application.

FIG. 1 is a diagram illustrating a wireless LAN system according to anembodiment of the present invention. The wireless LAN system includesone or more basic service sets (BSS) and the BSS represents a set ofapparatuses which are successfully synchronized with each other tocommunicate with each other. In general, the BSS may be classified intoan infrastructure BSS and an independent BSS (IBSS) and FIG. 1illustrates the infrastructure BSS between them.

As illustrated in FIG. 1, the infrastructure BSS (BSS1 and BSS2)includes one or more stations STA1, STA2, STA3, STA4, and STA5, accesspoints PCP/AP-1 and PCP/AP-2 which are stations providing a distributionservice, and a distribution system (DS) connecting the multiple accesspoints PCP/AP-1 and PCP/AP-2.

The station (STA) is a predetermined device including medium accesscontrol (MAC) following a regulation of an IEEE 802.11 standard and aphysical layer interface for a radio medium, and includes both anon-access point (non-AP) station and an access point (AP) in a broadsense. Further, in the present specification, a term ‘terminal’ may beused to refer to a non-AP STA, or an AP, or to both terms. A station forwireless communication includes a processor and a transceiver andaccording to the embodiment, may further include a user interface unitand a display unit. The processor may generate a frame to be transmittedthrough a wireless network or process a frame received through thewireless network and besides, perform various processing for controllingthe station. In addition, the transceiver is functionally connected withthe processor and transmits and receives frames through the wirelessnetwork for the station.

The access point (AP) is an entity that provides access to thedistribution system (DS) via wireless medium for the station associatedtherewith. In the infrastructure BSS, communication among non-APstations is, in principle, performed via the AP, but when a direct linkis configured, direct communication is enabled even among the non-APstations. Meanwhile, in the present invention, the AP is used as aconcept including a personal BSS coordination point (PCP) and mayinclude concepts including a centralized controller, a base station(BS), a node-B, a base transceiver system (BTS), and a site controllerin a broad sense.

A plurality of infrastructure BSSs may be connected with each otherthrough the distribution system (DS). In this case, a plurality of BSSsconnected through the distribution system is referred to as an extendedservice set (ESS).

FIG. 2 illustrates an independent BSS which is a wireless LAN systemaccording to another embodiment of the present invention. In theembodiment of FIG. 2, duplicative description of parts, which are thesame as or correspond to the embodiment of FIG. 1, will be omitted.

Since a BSS3 illustrated in FIG. 2 is the independent BSS and does notinclude the AP, all stations STA6 and STA7 are not connected with theAP. The independent BSS is not permitted to access the distributionsystem and forms a self-contained network. In the independent BSS, therespective stations STA6 and STA7 may be directly connected with eachother.

FIG. 3 is a block diagram illustrating a configuration of a station 100according to an embodiment of the present invention.

As illustrated in FIG. 3, the station 100 according to the embodiment ofthe present invention may include a processor 110, a transceiver 120, auser interface unit 140, a display unit 150, and a memory 160.

First, the transceiver 120 transmits and receives a wireless signal suchas a wireless LAN packet, or the like and may be embedded in the station100 or provided as an exterior. According to the embodiment, thetransceiver 120 may include at least one transmit/receive module usingdifferent frequency bands. For example, the transceiver 120 may includetransmit/receive modules having different frequency bands such as 2.4GHz, 5 GHz, and 60 GHz. According to an embodiment, the station 100 mayinclude a transmit/receive module using a frequency band of 6 GHz ormore and a transmit/receive module using a frequency band of 6 GHz orless. The respective transmit/receive modules may perform wirelesscommunication with the AP or an external station according to a wirelessLAN standard of a frequency band supported by the correspondingtransmit/receive module. The transceiver 120 may operate only onetransmit/receive module at a time or simultaneously operate multipletransmit/receive modules together according to the performance andrequirements of the station 100. When the station 100 includes aplurality of transmit/receive modules, each transmit/receive module maybe implemented by independent elements or a plurality of modules may beintegrated into one chip.

Next, the user interface unit 140 includes various types of input/outputmeans provided in the station 100. That is, the user interface unit 140may receive a user input by using various input means and the processor110 may control the station 100 based on the received user input.Further, the user interface unit 140 may perform output based on acommand of the processor 110 by using various output means.

Next, the display unit 150 outputs an image on a display screen. Thedisplay unit 150 may output various display objects such as contentsexecuted by the processor 110 or a user interface based on a controlcommand of the processor 110, and the like. Further, the memory 160stores a control program used in the station 100 and various resultingdata. The control program may include an access program required for thestation 100 to access the AP or the external station.

The processor 110 of the present invention may execute various commandsor programs and process data in the station 100. Further, the processor110 may control the respective units of the station 100 and control datatransmission/reception among the units. According to the embodiment ofthe present invention, the processor 110 may execute the program foraccessing the AP stored in the memory 160 and receive a communicationconfiguration message transmitted by the AP. Further, the processor 110may read information on a priority condition of the station 100 includedin the communication configuration message and request the access to theAP based on the information on the priority condition of the station100. The processor 110 of the present invention may represent a maincontrol unit of the station 100 and according to the embodiment, theprocessor 110 may represent a control unit for individually controllingsome component of the station 100, for example, the transceiver 120, andthe like. The processor 110 controls various operations of wirelesssignal transmission/reception of the station 100 according to theembodiment of the present invention. A detailed embodiment thereof willbe described below.

The station 100 illustrated in FIG. 3 is a block diagram according to anembodiment of the present invention, where separate blocks areillustrated as logically distinguished elements of the device.Accordingly, the elements of the device may be mounted in a single chipor multiple chips depending on design of the device. For example, theprocessor 110 and the transceiver 120 may be implemented while beingintegrated into a single chip or implemented as a separate chip.Further, in the embodiment of the present invention, some components ofthe station 100, for example, the user interface unit 140 and thedisplay unit 150 may be optionally provided in the station 100.

FIG. 4 is a block diagram illustrating a configuration of an AP 200according to an embodiment of the present invention.

As illustrated in FIG. 4, the AP 200 according to the embodiment of thepresent invention may include a processor 210, a transceiver 220, and amemory 260. In FIG. 4, among the components of the AP 200, duplicativedescription of parts which are the same as or correspond to thecomponents of the station 100 of FIG. 2 will be omitted.

Referring to FIG. 4, the AP 200 according to the present inventionincludes the transceiver 220 for operating the BSS in at least onefrequency band. As described in the embodiment of FIG. 3, thetransceiver 220 of the AP 200 may also include a plurality oftransmit/receive modules using different frequency bands. That is, theAP 200 according to the embodiment of the present invention may includetwo or more transmit/receive modules among different frequency bands,for example, 2.4 GHz, 5 GHz, and 60 GHz together. Preferably, the AP 200may include a transmit/receive module using a frequency band of 6 GHz ormore and a transmit/receive module using a frequency band of 6 GHz orless. The respective transmit/receive modules may perform wirelesscommunication with the station according to a wireless LAN standard of afrequency band supported by the corresponding transmit/receive module.The transceiver 220 may operate only one transmit/receive module at atime or simultaneously operate multiple transmit/receive modulestogether according to the performance and requirements of the AP 200.

Next, the memory 260 stores a control program used in the AP 200 andvarious resulting data. The control program may include an accessprogram for managing the access of the station. Further, the processor210 may control the respective units of the AP 200 and control datatransmission/reception among the units. According to the embodiment ofthe present invention, the processor 210 may execute the program foraccessing the station stored in the memory 260 and transmitcommunication configuration messages for one or more stations. In thiscase, the communication configuration messages may include informationabout access priority conditions of the respective stations. Further,the processor 210 performs an access configuration according to anaccess request of the station. The processor 210 controls variousoperations such as wireless signal transmission/reception of the AP 200according to the embodiment of the present invention. A detailedembodiment thereof will be described below.

FIG. 5 is a diagram illustrating a carrier sense multiple access(CSMA)/collision avoidance (CA) method used in wireless LANcommunication.

A terminal that performs a wireless LAN communication checks whether achannel is busy by performing carrier sensing before transmitting data.When a wireless signal having a predetermined strength or more issensed, it is determined that the corresponding channel is busy and theterminal delays the access to the corresponding channel. Such a processis referred to as clear channel assessment (CCA) and a level to decidewhether the corresponding signal is sensed is referred to as a CCAthreshold. When a wireless signal having the CCA threshold or more,which is received by the terminal, indicates the corresponding terminalas a receiver, the terminal processes the received wireless signal.Meanwhile, when a wireless signal is not sensed in the correspondingchannel or a wireless signal having a strength smaller than the CCAthreshold is sensed, it is determined that the channel is idle.

When it is determined that the channel is idle, each terminal havingdata to be transmitted performs a backoff procedure after an interframespace (IFS) time depending on a situation of each terminal, forinstance, an arbitration IFS (AIFS), a PCF IFS (PIFS), or the likeelapses. According to the embodiment, the AIFS may be used as acomponent which substitutes for the existing DCF IFS (DIFS). Eachterminal stands by while decreasing slot time(s) as long as a randomnumber assigned to the corresponding terminal during an interval of anidle state of the channel and a terminal that completely exhausts theslot time(s) attempts to access the corresponding channel. As such, aninterval in which each terminal performs the backoff procedure isreferred to as a contention window interval.

When a specific terminal successfully accesses the channel, thecorresponding terminal may transmit data through the channel. However,when the terminal which attempts the access collides with anotherterminal, the terminals which collide with each other are assigned withnew random numbers, respectively to perform the backoff procedure again.According to an embodiment, a random number newly assigned to eachterminal may be decided within a range (2*CW) which is twice larger thana range (a contention window, CW) of a random number which thecorresponding terminal is previously assigned. Meanwhile, each terminalattempts the access by performing the backoff procedure again in a nextcontention window interval and in this case, each terminal performs thebackoff procedure from slot time(s) which remained in the previouscontention window interval. By such a method, the respective terminalsthat perform the wireless LAN communication may avoid a mutual collisionfor a specific channel.

FIG. 6 is a diagram illustrating one embodiment of a wirelesscommunication scheme using a CCA technique.

In wireless communication, for instance, the wireless LAN communication,whether the channel is busy may be sensed through the CCA. In this case,the CCA methods including a signal detection (SD) method, an energydetection (ED) method, a correlation detection (CD) method, and the likemay be used.

First, the signal detection (CCA-SD) is a method that measures a signalstrength of a preamble of a wireless LAN (that is, 802.11) frame. Thismethod may stably detect the signal, but is disadvantageous in that themethod operates only in an initial part of a frame where the preamble ispresent. According to an embodiment, the signal detection may be used inthe CCA for a primary channel in a wideband wireless LAN. Next, theenergy detection (CCA-ED) is a method that senses energy of all signalsreceived with a specific threshold or more. This method may be used tosense a wireless signal in which the preamble is not normally sensed,for instance, signals such as Bluetooth, ZigBee, and the like. Further,the method may be used in the CCA for a secondary channel in which thesignal is not continuously tracked. Meanwhile, the correlation detection(CCA-CD) as a method that may sense a signal level even in the middle ofa wireless LAN frame uses that a wireless LAN signal has a periodicrepetition pattern of orthogonal frequency division multiplex (OFDM)signal. That is, the correlation detection method receives wireless LANdata for a predetermined time and thereafter, detects signal strengthsof the repetition patterns of an OFDM signal symbol.

According to the embodiment of the present invention, the access of theterminal to the channel may be controlled by using a predetermined CCAthreshold for each CCA method. In the embodiment of FIG. 6, a CCA-EDthreshold 10 represents a predetermined threshold in order to performthe energy detection and a CCA-SD threshold 30 represents apredetermined threshold in order to perform the signal detection.Further, receiving (RX) sensitivity 50 represents a minimum signalstrength at which the terminal may decode the wireless signal. Accordingto the embodiment, the RX sensitivity 50 may be set to a level which isthe same as or lower than the CCA-SD threshold 30 according to acapability and a configuration of the terminal. Further, the CCA-EDthreshold 10 may be set to a higher level than the CCA-SD threshold 30.For example, the CCA-ED threshold 10 and the CCA-SD threshold 30 may beset to −62 dBm and −82 dBm, respectively. However, the present inventionis not limited thereto and the CCA-ED threshold 10 and the CCA-SDthreshold 30 may be differently set according to whether the CCA-EDthreshold 10 and the CCA-SD threshold 30 are thresholds for the primarychannel, a bandwidth of a channel that performs the CCA, and the like.

According to the embodiment of FIG. 6, each terminal measures a receivedsignal strength indicator (RX RSSI) of the received wireless signal anddetermines a channel state based on a comparison between the measuredreceived signal strength and each set CCA threshold.

First, when a wireless signal 350 above the RX sensitivity 50, which isreceived in a specific channel has an RX RSSI of the CCA-SD threshold 30or less, it is determined that the corresponding channel is idle.Therefore, the received signal is not processed or protected in theterminal and each terminal may attempt the access to the correspondingchannel according to the method described in FIG. 5, and the like.

When a wireless LAN signal 330 having the RX RSSI of the CCA-SDthreshold 30 or more is received in a specific channel, it is determinedthat the corresponding channel is in a busy state. Accordingly, theterminal that receives the corresponding signal delays the access to thechannel. According to an embodiment, the terminal may determine whetherthe corresponding signal is the wireless LAN signal by using a signalpattern of a preamble part of the received wireless signal. According tothe embodiment of FIG. 6, even in case that a wireless LAN signal ofother BSS is received in addition to a wireless LAN signal of BSS whichis the same with the corresponding terminal, each terminal determinesthat the channel is in the busy state.

Meanwhile, when a wireless signal 310 having the RX RSSI of the CCA-EDthreshold 10 or more is received in a specific channel, it is determinedthat the corresponding channel is in the busy state. In case thatanother type of wireless signal (other than the wireless LAN signal) isreceived as well, the terminal determines that the corresponding channelis in the busy state, if the RX RSSI of the corresponding signal is theCCA-ED threshold 10 or more. Accordingly, the terminal that receives thecorresponding signal delays the access to the channel.

FIG. 7 illustrates one example of an overlapping BSS (OBSS) environment.In FIG. 7, in BSS-1 operated by AP-1, station 1 (STA-1) and station 2(STA-2) are associated with AP-1 and in BSS-2 operated by AP-2, station3 (STA-3) and station 4 (STA-4) are associated with AP-2. In theoverlapping BSS environment of FIG. 7, communication coverages of BSS-1and BSS-2 at least partially overlap with each other.

As illustrated in FIG. 7, when STA-3 transmits upload data to AP-2,STA-3 may continuously interfere with STA-2 of BSS-1 positioned adjacentthereto. In this case, interference which occurs while BSS-1 and BSS-2use the same frequency band (for example, 2.4 GHz, 5 GHz, or the like)and the same primary channel is referred to as co-channel interference(CCI). Further, interference which occurs while BSS-1 and BSS-2 use anadjacent primary channel is referred to as adjacent channel interference(ACI). The CCI or ACI may be received with a higher signal strength thanthe CCA threshold (e.g. CCA SD threshold) of STA-2 according to adistance between STA-2 and STA-3. When the interference is received bySTA-2 with the higher strength than the CCA threshold, STA-2 recognizesthat the corresponding channel is in the busy state to delaytransmission of the upload data to AP-1. However, since STA-2 and STA-3are stations that belong to different BSSs, when the CCA threshold ofSTA-2 increases, STA-2 and STA-3 may simultaneously upload to AP-1 andAP-2, respectively, thereby achieving an effect of spatial reuse.

Meanwhile, in FIG. 7, the transmission of the upload data by STA-3 inBSS-2 interferes even in STA-4 that belongs to the same BSS-2. In thiscase, when the CCA threshold of STA-4 increases similarly to STA-2,STA-3 and STA-4 that belong to the same BSS simultaneously transmit theupload data to AP-2, and as a result, a collision may occur. Therefore,in order to increase the CCA threshold for predetermined interference,it is needed to determine whether the corresponding interference iscaused by signals that belong to the same BSS or signals that belong todifferent BSSs. To this end, each terminal needs to verify a BSSidentifier of the received wireless LAN signal or other types ofinformation to distinguish the BSS. Further, it is preferable that theBSS information is verified within a short time while the CCA process isperformed.

FIGS. 8 to 13 are diagrams illustrating various embodiments of the CCAmethod according to the present invention. In the embodiments of FIGS. 8to 13, an area marked with a shade indicates a wireless signal which isreceived but disregarded, that is, not protected by the terminal. Inother words, when the wireless signal corresponding to the area markedwith the shade is received, the terminal determines that thecorresponding channel is in the idle state. Meanwhile, when a wirelesssignal corresponding to an area not marked with the shade is received,the terminal determines that the corresponding channel is in the busystate. In this case, the RX sensitivity may be set to the level which isthe same as or lower than the CCA-SD threshold according to thecapability and the configuration of the terminal. Further, the CCA-EDthreshold may be set to the higher level than the CCA-SD threshold.Individual processes described in FIG. 5 may be performed based on aresult of determining whether the channel is busy in each embodiment tobe described below.

In each of the embodiments of FIGS. 8 to 10, the terminal may measurethe RX RSSI of the received wireless signal and determine whether thecorresponding signal is the wireless LAN signal. When the receivedsignal is the wireless LAN signal having the BSS identifier informationaccording to various embodiments to be described below, the terminal mayextract the BSS identifier information from the corresponding signal anddetermine whether the extracted BSS identifier information is the sameas the BSS identifier information of the corresponding terminal.

First, according to the embodiment of FIG. 8, the CCA threshold for thecorresponding signal may be decided based on whether the receivedwireless signal is the wireless LAN signal having the BSS identifierinformation which is the same as the BSS identifier information of theterminal. In the embodiment of the present invention, the BSS identifierinformation of the terminal is BSS identifier information assigned tothe corresponding terminal and may represent, when the correspondingterminal is a non-AP STA, BSS identifier information of an AP which thecorresponding terminal is associated with or intends to be associatedwith. In this case, the terminal may receive the BSS identifierinformation from the AP and the received BSS identifier information maybe stored in the corresponding terminal.

Referring to FIG. 8, when a received wireless signal of a specificchannel is the wireless LAN signal having an RX RSSI of the RXsensitivity 50 or more and the CCA-SD threshold 30 or less, whether thechannel is busy is determined based on whether the corresponding signalis the wireless LAN signal having the same BSS identifier information asthat of the terminal. When the BSS identifier information extracted fromthe wireless signal is different from the BSS identifier information ofthe terminal (that is, in the case of OBSS wireless LAN signal 452), itis determined that the corresponding channel is in the idle state.However, when the BSS identifier information extracted from the wirelesssignal is the same as the BSS identifier information of the terminal(that is, in the case of MYBSS wireless LAN signal 454), it isdetermined that the corresponding channel is in the busy state.

Meanwhile, when the received wireless signal of the specific channel isa wireless LAN signal 430 having the RX RSSI between the CCA-SDthreshold 30 and the CCA-ED threshold 10, it is determined that thecorresponding channel is in the busy state. In this case, even in thecase where the corresponding signal is a wireless LAN signal havingdifferent BSS identifier information from that of the terminal inaddition to the case where the corresponding signal is the wireless LANsignal having the same BSS identifier information as that of theterminal, the terminal that receives the wireless LAN signal 430determines that the channel where the corresponding signal is receivedis in the busy state.

During the energy detection process, when the wireless signal of thespecific channel, which is received by the terminal is a wireless signal410 having the RX RSSI of the CCA-ED threshold 10 or more, it isdetermined that the corresponding channel is in the busy state. Asdescribed above, in case that another type of wireless signal (otherthan the wireless LAN signal) is received as well, the terminaldetermines that the corresponding channel is in the busy state, if theRX RSSI of the wireless signal is the CCA-ED threshold 10 or more.

As such, according to the embodiment of FIG. 8, the CCA thresholdapplied to the wireless LAN signal having the same BSS identifierinformation as that of the terminal may have a different level from theCCA threshold applied to the wireless LAN signal having the differentBSS identifier information from that of the terminal. According to anembodiment, the CCA threshold applied to the wireless LAN signal havingthe different BSS identifier information from that of the terminal isset to a higher level than the CCA threshold applied to the wireless LANsignal having the same BSS identifier information as that of theterminal. According to the embodiment of FIG. 8, as the CCA thresholdfor the wireless LAN signal having the different BSS identifierinformation from that of the terminal, the predetermined CCA-SDthreshold 30 may be adopted and as the CCA threshold for the wirelessLAN signal having the same BSS identifier information as that of theterminal, the level of the RX sensitivity 50 of the terminal may beadopted.

FIGS. 9 and 10 illustrate another embodiment of the CCA method using theBSS identifier information. In the embodiments of FIGS. 9 and 10,duplicative description of parts, which are the same as or correspond tothe embodiment of FIG. 8, will be omitted.

First, according to the embodiment of FIG. 9, the CCA threshold for thecorresponding signal may be decided based on whether the receivedwireless signal is the wireless LAN signal having the BSS identifierinformation which is the same as the BSS identifier information of theterminal.

Referring to FIG. 9, when the RX RSSI of a received wireless signal of aspecific channel is the RX sensitivity 50 or more and a first CCA-SDthreshold 40 or less, it is determined that the corresponding channel isin the idle state. In this case, both in the case where the receivedsignal is a wireless LAN signal 454 having the same BSS identifierinformation as that of the terminal and in the case where the receivedsignal is a wireless LAN signal 452 having the different BSS identifierinformation from that of the terminal, the terminal determines that thechannel where the corresponding signal is received is in the idle state.

However, when the received wireless signal of the specific channel isthe wireless LAN signal having the RX RSSI between the first CCA-SDthreshold 40 and a second CCA-SD threshold 20, whether the channel isbusy is determined based on whether the corresponding signal is thewireless LAN signal having the same BSS identifier information as thatof the terminal. When the BSS identifier information extracted from thewireless signal is different from the BSS identifier information of theterminal (that is, in the case of OBSS wireless LAN signal 442), it isdetermined that the corresponding channel is in the idle state. However,when the BSS identifier information extracted from the wireless signalis the same as the BSS identifier information of the terminal (that is,in the case of MYBSS wireless LAN signal 444), it is determined that thecorresponding channel is in the busy state. In the embodiment of FIG. 9,the second CCA-SD threshold 20 which is used to perform the signaldetection for the wireless LAN signal having the different BSSidentifier information from that of the terminal may be set to a levelwhich is larger than the first CCA-SD threshold 40 and equal to orsmaller than the CCA-ED threshold.

Meanwhile, when the received wireless signal of the specific channel isa wireless LAN signal 420 having an RX RSSI between the second CCA-SDthreshold 20 and the CCA-ED threshold 10, it is determined that thecorresponding channel is in the busy state. In this case, even in thecase where the corresponding signal is a wireless LAN signal havingdifferent BSS identifier information from that of the terminal inaddition to the case where the corresponding signal is the wireless LANsignal having the same BSS identifier information as that of theterminal, the terminal that receives the wireless LAN signal 420determines that the channel where the corresponding signal is receivedis in the busy state.

During the energy detection process, when the received wireless signalof the specific channel by the terminal is a wireless signal 410 havingthe RX RSSI of the CCA-ED threshold 10 or more, it is determined thatthe corresponding channel is in the busy state. As described above, incase that another type of wireless signal (other than the wireless LANsignal) is received as well, the terminal determines that thecorresponding channel is in the busy state, if the RX RSSI of thewireless signal is the CCA-ED threshold 10 or more.

As such, according to the embodiment of FIG. 9, the CCA thresholdapplied to the wireless LAN signal having the same BSS identifierinformation as that of the terminal may have a different level from theCCA threshold applied to the wireless LAN signal having the differentBSS identifier information from that of the terminal. That is, as theCCA threshold for the wireless LAN signal having the same BSS identifierinformation as that of the terminal, the predetermined first CCA-SDthreshold 40 may be adopted and as the CCA threshold for the wirelessLAN signal having the different BSS identifier information from that ofthe terminal, the predetermined second CCA-SD threshold 20 may beadopted. Herein, the second CCA-SD threshold 20 may be set to a levelwhich is higher than the first CCA-SD threshold 40 and equal to or lowerthan the CCA-ED threshold.

Next, according to the embodiment of FIG. 10, when the RX RSSI of areceived wireless signal of a specific channel is the RX sensitivity 50or more, the signal detection may be performed based on whether thecorresponding signal is the wireless LAN signal having the same BSSidentifier information as that of the terminal.

During the signal detection process, when the RX RSSI of the wirelesssignal received by the terminal is the RX sensitivity 50 or more and thewireless signal is a wireless LAN signal 453 having the same BSSidentifier information as that of the terminal, it is determined thatthe corresponding channel is in the busy state. However, when the RXRSSI of the received wireless signal is the RX sensitivity 50 or moreand the wireless signal is a wireless LAN signal 451 having differentBSS identifier information from that of the terminal, it is determinedthat the corresponding channel is in the idle state.

Meanwhile, during the energy detection process, when the wireless signalreceived by the terminal is the wireless signal 410 having the RX RSSIof the CCA-ED threshold 10 or more, it is determined that thecorresponding channel is in the busy state. The terminal determines thatthe corresponding channel is in the busy state regardless of whether thecorresponding signal is the wireless LAN signal having the same BSSidentifier information as that of the terminal and furthermore,regardless of whether the corresponding signal is the wireless LANsignal. Therefore, when the wireless LAN signal having the different BSSidentifier information from that of the terminal is received at a levelhigher than the CCA-ED threshold 10, it is determined that thecorresponding channel is in the busy state by the energy detectionprocess.

As such, according to the embodiment of FIG. 10, the terminal maydetermine whether the channel is busy based on whether the receivedwireless signal is the wireless LAN signal having the same BSSidentifier information as that of the terminal without using aseparately set CCA-SD threshold during the signal detection process.However, the terminal may avoid a collision with the wireless LAN signalhaving the different BSS identifier information from that of theterminal by using the predetermined CCA-ED threshold 10 for the energydetection.

FIGS. 11 to 13 are diagrams illustrating yet another embodiment of a CCAmethod using whether to obtain non-legacy wireless LAN information andBSS identifier information. In each embodiment of FIGS. 11 to 13, theterminal may measure the RX RSSI of the received wireless signal anddetermine whether the corresponding signal is the wireless LAN signal.When the received signal is the wireless LAN signal having the BSSidentifier information according to various embodiments to be describedbelow, the terminal may extract the BSS identifier information from thecorresponding signal and determine whether the extracted BSS identifierinformation is the same as the BSS identifier information of thecorresponding terminal.

Moreover, the terminal may obtain at least one of the legacy wirelessLAN information and the non-legacy wireless LAN information from thereceived wireless signal. As a result, the terminal may determinewhether the received wireless signal is a signal including only thelegacy wireless LAN information or a signal including both the legacywireless LAN information and the non-legacy wireless LAN information.According to an embodiment, the terminal may obtain at least one of thelegacy wireless LAN information and the non-legacy wireless LANinformation by using preamble information of the received wirelesssignal. The BSS identifier information of the wireless signal may beextracted from the non-legacy wireless LAN information when thenon-legacy wireless LAN information is obtained from the correspondingsignal. However, the present invention is not limited thereto andaccording to various embodiments described below the BSS identifierinformation of the wireless signal may be also extracted from the legacywireless LAN information. According to an embodiment of the presentinvention, the BSS identifier information which is referred to forexecuting the CCA is included in the non-legacy wireless LANinformation, while the non-legacy wireless LAN information may not beincluded in the received wireless signal. That is, when the receivedwireless signal does not include the BSS identifier information which isreferred to for executing the CCA according to the embodiment of thepresent invention, the BSS identifier information may not be extractedfrom the corresponding signal. In this case, the BSS identifierinformation of the corresponding signal for executing the CCA may be setto a predetermined value. In the embodiments of FIGS. 11 to 13,duplicative description of parts, which are the same as or correspond tothe aforementioned embodiments, will be omitted.

First, referring to FIG. 11, when a received wireless signal of aspecific channel is the wireless LAN signal having the RX RSSI of the RXsensitivity 50 or more and the first CCA-SD threshold 40 or less,whether the channel is busy is determined based on whether thecorresponding signal is the wireless LAN signal having the same BSSidentifier information as that of the terminal.

When the BSS identifier information extracted from the wireless signalis different from the BSS identifier information of the terminal (thatis, in the case of OBSS wireless LAN signal), it is determined that thecorresponding channel is in the idle state. In this case, the OBSSwireless LAN signal 552 may be divided into an OBSS non-legacy wirelessLAN signal in which the non-legacy wireless LAN information may beobtained from the corresponding signal and an OBSS legacy wireless LANsignal in which the non-legacy wireless LAN information is not obtainedfrom the corresponding signal. The terminal determines that thecorresponding channel is in the idle state both in the case where theOBSS non-legacy wireless LAN signal is received and in the case wherethe OBSS legacy wireless LAN signal is received.

On the contrary, when the BSS identifier information extracted from thewireless signal is the same as the BSS identifier information of theterminal (that is, in the case of MYBSS wireless LAN signal), it isdetermined that the corresponding channel is in the busy state.Similarly, the MYBSS wireless signal may be divided into a MYBSSnon-legacy wireless LAN signal 558 in which the non-legacy wireless LANinformation may be obtained from the corresponding signal and an MYBSSlegacy wireless LAN signal 556 in which the non-legacy wireless LANinformation is not obtained from the corresponding signal. The terminaldetermines that the corresponding channel is in the busy state both inthe case where the MYBSS non-legacy wireless LAN signal 558 is receivedand in the case where the MYBSS legacy wireless LAN signal 556 isreceived.

Meanwhile, when the received wireless signal of the specific channel isthe wireless LAN signal having the RX RSSI between the first CCA-SDthreshold 40 and the second CCA-SD threshold 20, whether the channel isbusy is determined based on whether the corresponding signal includesthe non-legacy wireless LAN information and whether the correspondingsignal has the same BSS identifier information as that of the terminal.According to an embodiment, the first CCA-SD threshold 40 may be set tothe same level as the CCA-SD threshold applied to the legacy terminaland the second CCA-SD threshold 20 may be set to a higher level than thefirst CCA-SD threshold 40 and equal to or lower than the CCA-EDthreshold.

When the non-legacy wireless LAN information is obtained from thewireless signal and the BSS identifier information of the correspondingsignal is different from the BSS identifier information of the terminal(that is, in the case of non-legacy OBSS signal 542), it is determinedthat the corresponding channel is in the idle state. However, in othercases, when the non-legacy wireless LAN information is not obtained fromthe wireless signal (that is, a legacy signal) or the BSS identifierinformation of the corresponding signal is the same as the BSSidentifier information of the terminal (that is, a MYBSS signal), it isdetermined that the corresponding channel is in the busy state. In moredetail, the case where it is determined that the channel is in the busystate includes i) a case where the non-legacy wireless LAN informationis not obtained from the wireless signal and the BSS identifierinformation of the corresponding signal is different from the BSSidentifier information of the terminal (that is, in the case of legacyOBSS signal 544), ii) a case where the non-legacy wireless LANinformation is not obtained from the wireless signal and the BSSidentifier information of the corresponding signal is the same as theBSS identifier information of the terminal (that is, in the case oflegacy MYBSS signal 546), and iii) a case where the non-legacy wirelessLAN information is obtained from the wireless signal and the BSSidentifier information of the corresponding signal is the same as theBSS identifier information of the terminal (that is, in the case ofnon-legacy MYBSS signal 548).

That is, when the non-legacy wireless LAN information is not obtainedfrom the wireless signal, it is determined that the correspondingchannel is in the busy state, but when the non-legacy wireless LANinformation is obtained from the wireless signal, whether the channel isbusy is determined based on whether the BSS identifier information ofthe corresponding signal is the same as the BSS identifier informationof the terminal. Therefore, according to the embodiment of the presentinvention, when the non-legacy wireless LAN information is obtained fromthe wireless signal, whether the corresponding channel is busy may bedetermined based on the BSS identifier information of the wirelesssignal. According to an embodiment, when the non-legacy wireless LANinformation is not obtained from the wireless signal, the BSS identifierinformation which is referred to for executing the CCA of the presentinvention may not be extracted from the corresponding signal. In thiscase, the terminal may determine that the channel is in the busy stateregardless of whether the BSS identifier information is extracted fromthe corresponding signal.

The signal detection process may be performed by referring to thepreamble of the received wireless signal. According to an embodiment,when it is determined that the channel is in the busy state during thesignal detection process, even though the RX RSSI decreases to the firstCCA-SD threshold 40 or less while receiving the wireless signal which isbeing protected, the terminal may not access the channel during a frametransmission time of the wireless signal.

Meanwhile, when the received wireless signal of the specific channel isa wireless LAN signal 520 between the second CCA-SD threshold 20 and theCCA-ED threshold 10, it is determined that the corresponding channel isin the busy state. In this case, the terminal that receives the wirelessLAN signal 520 determines that a channel where the corresponding signalis received is in the busy state regardless of whether the non-legacywireless LAN information is obtained from the corresponding signal andfurthermore, regardless of whether the corresponding signal is thewireless LAN signal having the same BSS identifier information as thatof the terminal.

During the energy detection process, when the received wireless signalof the specific channel by the terminal is a wireless signal 510 of theCCA-ED threshold 10 or more, it is determined that the correspondingchannel is in the busy state. As described above, in case that anothertype of wireless signal (other than the wireless LAN signal) is receivedas well, the terminal determines that the corresponding channel is inthe busy state, if the RX RSSI of the wireless signal is the CCA-EDthreshold 10 or more.

Next, according to the embodiment of FIG. 12, when a received wirelesssignal of a specific channel is the wireless LAN signal having the RXsensitivity 50 or more and the RX RSSI of the first CCA-SD threshold 40or less, whether the channel is busy is determined based on whether thecorresponding signal includes the non-legacy wireless LAN informationand whether the corresponding signal has the same BSS identifierinformation as that of the terminal.

When the non-legacy wireless LAN information is obtained from thewireless signal and the BSS identifier information of the correspondingsignal is the same as the BSS identifier information of the terminal(that is, in the case of non-legacy MYBSS signal 558), it is determinedthat the corresponding channel is in the busy state. However, in othercases, when the BSS identifier information of the wireless signal isdifferent from the BSS identifier information of the terminal (that is,OBSS signal) or the non-legacy wireless LAN information is not obtainedfrom the corresponding signal (that is, legacy signal), it is determinedthat the corresponding channel is in the idle state. In more detail, thecase where it is determined that the channel is in the idle stateincludes i) a case where the non-legacy wireless LAN information isobtained from the wireless signal and the BSS identifier information ofthe corresponding signal is different from the BSS identifierinformation of the terminal (that is, in the case of non-legacy OBSSsignal 552), ii) a case where the non-legacy wireless LAN information isnot obtained from the wireless signal and the BSS identifier informationof the corresponding signal is different from the BSS identifierinformation of the terminal (that is, in the case of legacy BSS signal554), and iii) a case where the non-legacy wireless LAN information isnot obtained from the wireless signal and the BSS identifier informationof the corresponding signal is the same as the BSS identifierinformation of the terminal (that is, in the case of legacy MYBSS signal556).

That is, when the non-legacy wireless LAN information is not obtainedfrom the wireless signal, it is determined that the correspondingchannel is in the idle state, but when the non-legacy wireless LANinformation is obtained from the wireless signal, whether the channel isbusy is determined based on whether the BSS identifier information ofthe corresponding signal is the same as the BSS identifier informationof the terminal. According to the embodiment of FIG. 12, when thenon-legacy wireless LAN information is obtained from the wireless signaland the BSS identifier information of the corresponding signal isdifferent from the BSS identifier information of the terminal, apredetermined CCA threshold 20 may be used for the CCA of thecorresponding channel. However, when the non-legacy wireless LANinformation is obtained from the wireless signal and the BSS identifierinformation of the corresponding signal is the same as the BSSidentifier information of the terminal, in the case where thecorresponding signal has the RX RSSI of the RX sensitivity 50 or more,it may be determined that the corresponding channel is in the busy statewithout setting a separate CCA threshold. According to an embodiment,when the non-legacy wireless LAN information is not obtained from thewireless signal, the BSS identifier information which is referred to forexecuting the CCA of the present invention may not be extracted from thecorresponding signal. In this case, the terminal may determine that thechannel is in the idle state regardless of whether the BSS identifierinformation is extracted from the corresponding signal.

According to the embodiment of FIG. 12, even though the BSS identifierinformation which is referred to for executing the CCA is included inthe non-legacy wireless LAN information and the received wireless LANsignal does not include the non-legacy wireless LAN information, the CCAmay be efficiently executed. That is, when the received wireless signalis the legacy wireless LAN signal from which the BSS identifierinformation is not extracted, it is determined that the correspondingchannel is in the idle state or the busy state in a lump according tothe RX RSSI of the corresponding signal to minimize a time delayrequired to determine whether the BSS identifier of the legacy wirelessLAN signal is actually the same as the BSS identifier of the terminal.That is, only when the received wireless signal is the non-legacywireless LAN signal, the terminal additionally verifies the BSSidentifier information to determine whether the channel is in theidle/busy state.

Next, according to the embodiment of FIG. 13, when the RX RSSI of areceived wireless signal of a specific channel is the RX sensitivity 50or more and the first CCA-SD threshold 40 or less, it is determined thatthe corresponding channel is in the idle state. In this case, theterminal determines that the corresponding channel is in the idle stateregardless of whether the received signal includes the non-legacywireless LAN information and whether the received signal has the sameBSS identifier information as that of the terminal. Further, accordingto the embodiment of FIG. 13, when the non-legacy wireless LANinformation is obtained from the wireless signal and the BSS identifierinformation of the corresponding signal is the same as the BSSidentifier information of the terminal, a first CCA threshold may beused for the CCA of the corresponding channel. However, when thenon-legacy wireless LAN information is obtained from the wireless signaland the BSS identifier information of the corresponding signal isdifferent from the BSS identifier information of the terminal, a secondCCA threshold having a higher level than the first CCA threshold may beused for the CCA of the corresponding channel.

According to the embodiment of FIG. 13, when the wireless LAN signalhaving the same BSS identifier information as that of the terminal isreceived, a problem of unfairness in that different CCA thresholds areapplied according to whether the corresponding wireless LAN signalincludes the non-legacy wireless LAN information may be resolved. Thatis, CCA thresholds for the legacy MYBSS signal and the non-legacy MYBSSsignal are similarly applied to maintain fairness for channel occupationbetween a legacy terminal and a non-legacy terminal.

Meanwhile, in the embodiments of FIGS. 12 and 13, when the wirelesssignal having the RX RSSI of the first CCA-SD threshold 40 or more isreceived, a CCA process may be performed similarly to the embodiment ofFIG. 11.

FIG. 14 is a diagram illustrating a frame structure of a wireless LANsignal according to an embodiment of the present invention. Referring toFIG. 14, the wireless LAN signal according to the embodiment of thepresent invention may include a legacy preamble 710 for a legacyterminal (e.g. a terminal such as 802.11a/g, or the like) and anon-legacy preamble 720 for a non-legacy terminal (e.g. a terminal of802.11ax). First, the legacy preamble 710 may include legacy wirelessLAN information which the legacy terminal is able to decode, forinstance, L-STF, L-LTF, L-SIG fields, and the like. Next, the non-legacypreamble 720 may include non-legacy wireless LAN information which onlythe non-legacy terminal is able to decode and the non-legacy wirelessLAN information may not be decoded by the legacy terminal. Meanwhile,the legacy preamble 710 may include at least some of the non-legacywireless LAN information which the non-legacy terminal is able to decodeaccording to the embodiment. Moreover, the non-legacy preamble 720 mayinclude at least one field of the legacy preamble 710, for instance,repeated information of a part or the entirety of the L-SIG field.

According to an embodiment of the present invention, the BSS identifierinformation which is referred to for executing the CCA may be includedin the non-legacy preamble 720 as the non-legacy wireless LANinformation. In this case, the BSS identifier information may beextracted from a predetermined bit filed of the non-legacy preamble 720.Meanwhile, according to another embodiment of the present invention, theBSS identifier information may be extracted from additional informationof the legacy preamble 710. For example, the legacy preamble 710 mayinclude the non-legacy wireless LAN information through an additionalsubcarrier set, and the like a described below and the BSS identifierinformation may be obtained from the non-legacy wireless LAN informationincluded in the legacy preamble 710. According to yet another embodimentof the present invention, the BSS identifier information may beextracted from a predetermined bit field of the legacy preamble 710. Inthis case, the predetermined bit field of the legacy preamble 710 may bea bit field set for the legacy terminal and a value of the correspondingbit field may be used as the BSS identifier information under a specificcondition as described below.

FIG. 15 illustrates a method for representing the BSS identifierinformation according to an embodiment of the present invention.According to the embodiment of the present invention, the BSS identifierinformation may be represented as a predetermined bit filed of thenon-legacy preamble 720 of FIG. 14. According to an embodiment of thepresent invention, the BSS identifier information may be abbreviatedinformation of a BSS identifier assigned to each BSS and may beinformation having smaller bits than the actual BSS identifier. Forexample, when the BSS identifier is represented as information of 24bits in a specific wireless LAN system, the BSS identifier informationmay be represented as a bit filed having a predetermined length in therange of 1 bit to 23 bits. In the preset invention, the BSS identifierinformation is information acquired by classifying the actual BSSidentifier into a predetermined category and may be named even as a BSScolor. A method for obtaining a BSS color abbreviated from the BSSidentifier includes a method using a combination of bit values at apredetermined location of the BSS identifier, a method using a resultvalue acquired by applying a predetermined Hash function to the BSSidentifier, and the like.

FIG. 15 as an embodiment thereof illustrates a result of acquiring theBSS color by using last 3 bit values of the BSS identifier. As such, theBSS color may be included in the preamble of the wireless LAN signal asinformation of a smaller amount than the actual BSS identifier, and as aresult, each terminal may efficiently determine whether the receivedwireless LAN signal is a signal having the same BSS identifier as thecorresponding terminal within a short time. The BSS identifierinformation may be represented as a predetermined bit of the non-legacypreamble.

Meanwhile, according to an embodiment of the present invention, thenon-legacy preamble 720 may include the repeated L-SIG field and therepeated L-SIG field may be configured to have at least the some bitsidentical with the L-SIG field of the legacy preamble 710. In this case,the bits different from the L-SIG field of the legacy preamble 710 amongthe bits of the repeated L-SIG field may represent the BSS identifierinformation, bandwidth information of the system, non-legacy wirelessLAN system information, channel information, and the like.

According to an additional embodiment of the present invention,additional information may be transmitted through a modulation methodapplied to the repeated L-SIG field. That is, the repeated L-SIG fieldmay be represented as the same modulation value as the L-SIG field ofthe legacy preamble 710 or otherwise expressed as a counter modulationvalue. Herein, the counter modulation value may be represented through aphase shift between modulation symbols transmitted to the L-SIG of thelegacy preamble 710 and modulation symbols of the repeated L-SIG and theadditional information may be transmitted through a phase shift amount.In detail, when the L-SIG of the legacy preamble 710 and the repeatedL-SIG are multiplied by (1, 1) to be transmitted, the symbols of bothfields have the same phase and when the L-SIG of the legacy preamble 710and the repeated L-SIG are multiplied by (1, −1) to be transmitted, aphase shift of 180° occurs between the symbols of the repeated L-SIG andthe symbols of the legacy preamble 710. In this case, specific flaginformation for the non-legacy wireless LAN information may bedetermined according to whether the repeated L-SIG field is representedas the same modulation value as the L-SIG field of the legacy preamble710, for example, whether a SIG-A field of the non-legacy preamble has avariable length, whether a SIG-B field is included in the non-legacypreamble, whether a specific bit field of the non-legacy preamble(alternatively, legacy preamble) represents the BSS identifierinformation, and the like may be determined.

FIGS. 16 and 17 as another embodiment of the present inventionillustrate a method for obtaining the non-legacy wireless LANinformation by using an additional subcarrier set of the wireless LANsignal.

First, FIG. 16 illustrates an embodiment of a subcarrier configurationused in the legacy preamble of the wireless LAN signal. According to anembodiment of the present invention, the subcarrier set of the legacypreamble of the non-legacy wireless LAN signal may be configuredequivalent to the subcarrier set of the legacy wireless LAN signal. Thatis, the subcarrier set of the legacy preamble may be constituted by atotal of 52 subcarrier including 4 pilot subcarriers and 48 datasubcarriers in a bandwidth of 20 MHz. In this case, when numbers ofrespective subcarriers are set to −26, −25, . . . , −2, −1, 1, 2, . . ., 25, and 26, subcarriers having numbers of −21, −7, 7, and 21 are usedas the pilot subcarriers and subcarriers of the residual numbers areused as the data subcarriers. Such a basic configuration of thesubcarrier is required to maintain mutual compatibility in anenvironment in which the legacy wireless LAN system (e.g. 802.11 a/g)and the non-legacy wireless LAN system (e.g. 802.11 ax, or the like)coexist. That is, the legacy preamble of the non-legacy wireless LANsignal as well as the legacy wireless LAN signal has the subcarrierconfiguration illustrated in FIG. 16 to provide backward compatibilityto the legacy terminal.

FIG. 17 illustrates an embodiment of the subcarrier configuration usedin the non-legacy wireless LAN signal. An additional subcarrier may beused without interference of an adjacent bandwidth in the non-legacywireless LAN system with the development of a filter or an amplifierused in the terminal. Referring to FIG. 17, the subcarrier of thenon-legacy wireless LAN signal according to the embodiment of thepresent invention may be configured to include a first subcarrier set800 and a second subcarrier set 820. In more detail, the firstsubcarrier set 800 may be configured equivalent to the subcarrier set ofthe legacy wireless LAN signal illustrated in FIG. 16. Further, thesecond subcarrier set 820 as a subcarrier set different from the firstsubcarrier set 800 may include 4 extra subcarriers, two at each higherand lower indices of the first subcarrier set 800, according to anembodiment. According to the embodiment of FIG. 17, since the non-legacywireless LAN signal uses pilot subcarriers at the same location and ofthe same number as the legacy wireless LAN signal, 52 data subcarrierswhich increase from the existing 48 subcarriers by 4 may be used.According to an embodiment, the subcarrier configuration may be usedafter a legacy preamble part of the non-legacy wireless LAN signal. Thenon-legacy terminal may obtain information through a total of 56subcarriers in the respective non-legacy preamble and data field of thereceived non-legacy wireless LAN signal.

According to the embodiment of the present invention, the secondsubcarrier set 820 included in the non-legacy preamble may represent theBSS identifier information, the bandwidth information of the system, thenon-legacy wireless LAN system information, the channel information, andthe like. In this case, a separate parity bit for parity check of thesecond subcarrier set 820 may be included in the non-legacy preamble.According to an embodiment, when the non-legacy preamble includes therepeated L-SIG field as described above, the BSS identifier information,the bandwidth information of the system, the non-legacy wireless LANsystem information, the channel information, and the like may berepresented through the second subcarrier set 820 of the repeated L-SIGfield.

Meanwhile, according to another embodiment of the present invention, thesubcarrier configuration of FIG. 17 may be extensively applied to thelegacy preamble of the non-legacy wireless LAN signal. That is, thelegacy preamble of the non-legacy wireless LAN signal may additionallyinclude the second subcarrier set 820 and transfer the non-legacywireless LAN information through the second subcarrier set 820. In thiscase, the legacy terminal may not obtain information from the secondsubcarrier set 820, but the non-legacy terminal may obtain additionalinformation from the second subcarrier set 820 of the legacy preamble.

For example, when it is assumed that the second subcarrier set 820additionally used in the legacy preamble includes 4 subcarriers, theindices (that is, subcarrier numbers) of the corresponding subcarriersmay be set to −28, −27, 27, and 28, respectively as illustrated in FIG.17. In this case, when a BPSK modulation scheme is used in the legacypreamble and the same modulation scheme is applied to the secondsubcarrier set, information of a total of 4 bits may be additionallytransmitted. Similarly, when a QPSK modulation scheme is applied to thesecond subcarrier set, information of a total of 8 bits may beadditionally transmitted. In this case, the parity bit for parity checkof the second subcarrier set included in the legacy preamble may beincluded in the non-legacy preamble.

According to an additional embodiment of the present invention, onlysome of total bits which may be represented by the second subcarrier set820 of the legacy preamble may be used for transmitting the additionalinformation. For example, only some bits of the second subcarrier set820 may be used for transmitting the additional information forcompatibility with the parity check of the legacy preamble. That is, theinformation added to the second subcarrier set 820 may be configured tohave even parities for compatibility with the parity bit used in theexisting L-SIG and when the BPSK modulation scheme is used, informationwhich may be transferred through the second subcarrier set 820 may beinformation of a total of 3 bits such as 1010, 0101, 1100, 0011, 1001,0110, 1111, and 0000.

According to another embodiment, a specific bit of the second subcarrierset 820 may be used as the parity check bit and the residual bits may beused for transmitting the additional information. For example, 3 bitsamong 4 bits of the second subcarrier set 820 may be used fortransmitting the additional information and 1 bit may be used as theparity bit. In this case, the parity bit of the second subcarrier set820 may be used for the parity check for bits added by the secondsubcarrier set 820 or otherwise used for parity check of the entireL-SIG including the second subcarrier set 820. In this case, the paritycheck with respect to the legacy wireless LAN signal may be performed byusing the existing parity bit of the L-SIG and the parity check withrespect to the non-legacy wireless LAN signal is performed by using boththe existing parity bit of the L-SIG and the parity bit of the secondsubcarrier set 820 to achieve parity check with higher-reliability.According to yet another embodiment, the parity check with respect tothe non-legacy wireless LAN information added by the second subcarrierset 820 may be performed by using a reserved bit of the L-SIG.

When the additional information for the non-legacy terminal istransmitted through the second subcarrier set 820 of the legacypreamble, the non-legacy terminal may more rapidly obtain the additionalinformation in the legacy preamble of the received wireless LAN signal,thus an initial access delay or detection of a preamble, a header, and apacket which are not required may be reduced by using the obtainedadditional information. Further, according to the embodiment of thepresent invention, the non-legacy terminal may obtain the non-legacywireless LAN information from the second subcarrier set 820 of thelegacy preamble and the non-legacy wireless LAN information obtained inthat case may include the BSS identifier information, the bandwidthinformation of the system, the non-legacy wireless LAN systeminformation, the channel information, and the like. When the non-legacyterminal obtains the second subcarrier set 820 in the legacy preamble ofthe received wireless LAN signal, the non-legacy terminal may recognizethat the corresponding wireless LAN signal includes the non-legacywireless LAN information.

In the embodiment of FIG. 17, the embodiment in which 4 additional datasubcarriers are included in the second subcarrier set 820 is described,but the present invention is not limited thereto and different numbersof subcarriers may be included in a second subcarrier set 820. Further,the embodiment of FIG. 17 may be applied to a case where otherbandwidths including 40 MHz, 80 MHz, and 160 MHz are used as well as acase where a bandwidth of the wireless LAN signal is 20 MHz.

FIG. 18 as yet another embodiment illustrates a method for representingthe non-legacy wireless LAN information by using a predetermined bitfield of the legacy preamble.

According to an additional embodiment of the present invention, thenon-legacy wireless LAN information may be extracted from thepredetermined bit field of the legacy preamble under a specificcondition. FIG. 18 as an embodiment thereof illustrates a rate bit fieldincluded in the L-SIG of the legacy preamble. As illustrated in FIG. 18,a 4-th bit in the rate bit filed of the existing legacy preamble iscontinuously set to 1. Therefore, information on a data rate, amodulation scheme, and a coding rate of the legacy wireless LAN signalmay be obtained through former 3 bit values in the rate bit field.Accordingly, according to the embodiment of the present invention,whether the corresponding rate bit field represents the non-legacywireless LAN information may be decided based on the 4-th bit value ofthe rate bit field. That is, when the 4-th bit of the rate bit field hasa value of 1, the corresponding rate bit field may represent theexisting information, that is, the data rate, the modulation scheme, andthe coding rate. However, when the 4-th bit of the rate bit field has avalue of 0, the corresponding rate bit field may represent thenon-legacy wireless LAN information.

When it is determined that the rate bit field includes the non-legacywireless LAN information, the BSS identifier information may beextracted from former 3 bit values of the corresponding rate bit fieldas illustrated in FIG. 18. However, the present invention is not limitedthereto and the non-legacy wireless LAN information such as bandwidthinformation, channel information, an association identifier (AID), andthe like of the non-legacy wireless LAN signal may be extracted from therate bit field. In this case, actual rate information for the non-legacyterminal may be transmitted through the non-legacy preamble. Meanwhile,even when the rate bit field includes the non-legacy wireless LANinformation, the legacy terminal may analyze the non-legacy wireless LANinformation as rate information. For such a situation, by appropriatelyconfiguring a length field of the L-SIG, the legacy terminals mayperform a transmission delay (NAV configuration, and the like) by usingL-SIG length information of other terminal packets when the transmissiondelay is required due to transmission of other terminals. In moredetail, since the length field of the legacy preamble represents thesize (the number of bytes) of transmission data, when information on thenumber of transmitted bits per OFDM symbol is obtained based on amodulation and coding scheme (MCS) and the length field is divided bythe obtained information, the number of required OFDM symbols isdetermined. In this case, the network allocation vector (NAV)configuration may be performed according to the obtained number of OFDMsymbols, and when the rate bit field is used as the non-legacy wirelessLAN information in accordance with the embodiment of the presentinvention, the NAV may be configured as large as a required length byadjusting the length field.

As such, according to the embodiment of the present invention, based oninformation on predetermined specific bits of the legacy preamble,whether the corresponding legacy preamble includes the non-legacywireless LAN information may be determined. When it is determined thatthe legacy preamble includes the non-legacy wireless LAN information,the non-legacy wireless LAN information such as the BSS identifierinformation, and the like may be extracted from the predetermined bitfield of the legacy preamble, for instance, the rate bit field.

Meanwhile, according to an additional embodiment of the presentinvention, information on more bits may be secured by using acombination of the second subcarrier set of the legacy preamble and thespecific bit field (that is, rate bit field), and as a result, thenon-legacy wireless LAN information may be transferred. For example,when the legacy preamble is configured to additionally include thesecond subcarrier set, the non-legacy terminal may determine that thecorresponding legacy preamble includes the non-legacy wireless LANinformation and extract the BSS identifier information from all or someof 4 bits in the rate bit field. Furthermore, when the legacy preambleis configured to additionally include the second subcarrier set, thenon-legacy terminal may analyze the entirety of the L-SIG bit field ofthe legacy preamble as the non-legacy wireless LAN information. As such,according to the embodiment of FIG. 18, since at least some ofnon-legacy wireless LAN information such as the BSS identifierinformation, and the like may be obtained from the legacy preamblebefore checking the non-legacy preamble, the CCA may be performed withina shorter time.

FIG. 19 is a diagram illustrating the unfairness problem of a legacyterminal that may occur if an adjusted CCA threshold is used for channelaccess according to an embodiment of the present invention. According tothe embodiment of FIG. 19 and the following embodiments, a MYBSSTransmitter (MT) and a MYBSS Receiver (MR) represent a transmissionterminal and a reception terminal of a first BSS (e.g., a MYBSS),respectively, and an OBSS Transmitter (OT) and an OBSS Receiver (OR)represent a transmission terminal and a reception terminal of a secondBSS (e.g., an OBSS) different from the first BSS. It is also assumedthat an MT, an MR, an OT and an OR are non-legacy terminals and an L isa legacy terminal.

As shown in FIG. 19, in the OBSS, the terminal OT may transmit dataO_DATA to the terminal OR and the terminal OR may transmit a responsemessage O_ACK to the terminal OT in response to the received dataO_DATA. In this case, if the received signal strength of the wirelesssignal O_DATA is higher than the first CCA threshold CCA-SD 1, thelegacy terminal L located around the terminals OT and OR determines thata channel is busy, and do not perform channel access. In this case, thechannel access delay period 810 of the legacy terminal L may be set to atime until the transmission of the response message O_ACK of theterminal OR is completed.

On the other hand, the terminal MT of the MYBSS different from the OBSSdetermines whether the channel is busy based on the received signalstrength of the wireless signal O_DATA and BSS identifier information ofthe corresponding signal, as in the above embodiment. That is, if theBSS identifier information of the received wireless signal O_DATA isdifferent from the BSS identifier information of the correspondingterminal, the terminal MT performs CCA based on the second CCA thresholdCCA-SD 2. In this case, the second CCA threshold CCA-SD 2 has a higherlevel than the first CCA threshold CCA-SD 1 used in the legacy terminal.Therefore, if it is assumed that O_DATA is received respectively by thelegacy terminal L and the non-legacy terminal MT as the received signalstrength between the first CCA threshold CCA-SD 1 and the second CCAthreshold CCA-SD 2, the channel access of the legacy terminal L ispostponed but the channel access of the non-legacy terminal MT isallowed.

In such a way, if the received signal strength of O_DATA is lower thanthe second CCA threshold CCA-SD 2, the terminal MT determines that thechannel is in an idle state and performs channel access. That is, theterminal MT performs a backoff procedure and transmits data MY_DATA whenthe backoff counter of the backoff procedure expires. In addition, theterminal MR receiving MY_DATA from the terminal MT transmits a responsemessage MY_ACK in response thereto. In this case, if the transmission ofthe wireless signals MY_DATA and MY_ACK exchanged between the terminalsMT and MR ends later than a channel access delay period 810 set in thelegacy terminal L, the legacy terminal L may not access the channel evenduring an additional period 820 after the channel access delay period810. Such a problem may occur not only in a single MAC Protocol DataUnit (MPDU) transmission but also in transmission situations based ontransmission opportunity (TXOP) or aggregate MPDU (A-MPDU).

FIGS. 20 to 23 illustrate the data transmission method of a non-legacyterminal for solving the channel access delay problem of a legacyterminal.

First, FIG. 20 illustrates a frame structure of a non-legacy wirelessLAN signal according to an embodiment of the present invention.Referring to FIG. 20, the non-legacy wireless LAN signal includes apreamble 910, an L-SIG field 920 for a legacy terminal (e.g., an802.11a/g terminal), a HEW-SIG field 930 for a non-legacy terminal(e.g., an 802.11ax terminal), and a MAC header 940. In an embodiment ofthe present invention, the L-SIG field 920 may represent at least aportion of a legacy preamble and the HEW-SIG field 930 may represent atleast a portion of a non-legacy preamble. According to an embodiment ofthe present invention, the L-SIG field 920, the HEW-SIG field 930, andthe MAC header 940 each includes length information indicating thetransmission length of data. In the present invention, lengthinformation included in the L-SIG 920 is referred to as LEN-1, lengthinformation included in the HEW-SIG 930 is referred to as LEN-2, lengthinformation included in the MAC header 940 is referred to as LEN-3,respectively. According to an embodiment of the present invention, LEN-1may represent a length field of L-SIG 920, LEN-2 may represent a lengthfield of HEW-SIG 930, and LEN-3 may represent a duration field of theheader 940, but the present invention is not limited thereto.

According to an embodiment of the present invention, LEN-1 representslength information of a corresponding frame. In this case, the lengthinformation of the frame may be represented by time information requiredfor frame transmission, or may be represented by data size (byte number)information in which the time required for the transmission can beinferred in combination with other information. On the other hand, LEN-2may represent length information until the transmission of acorresponding frame and frames related thereto are completed. Here, therelated frames include a subsequent frame of the corresponding frame.According to another embodiment of the present invention, LEN-2 mayrepresent length information until the next contention window intervalis activated after the transmission of a corresponding frame and framesrelated thereto is completed. Here, the related frames include not onlya subsequent frame of the corresponding frame but also a response (ACK)frame corresponding to each transmitted frame. In such a way, the lengthinformation represented by LEN-2 is referred to as “total transmissionlength information” in an embodiment of the present invention. Accordingto an embodiment, LEN-2 may represent information of the duration fieldof the corresponding frame or may represent length information oftransmission opportunity (TXOP) guaranteed to a terminal transmittingthe corresponding frame. Finally, LEN-3 represents an arbitrary lengthdefined by MAC.

On the other hand, information represented by LEN-1 and LEN-2 is notlimited to the above description, and may be modified by other methods.That is, in an embodiment of the present invention, at least one ofLEN-1 and LEN-2 may represent the total transmission length information.If LEN-1 represents length information (e.g., total transmission lengthinformation) that exceeds the length of a corresponding frame, thecorresponding frame may further include L-SIG Length Extend (LLE)information indicating the length information. In the same manner, ifLEN-2 represents length information (e.g., total transmission lengthinformation) that exceeds the length of a corresponding frame, thecorresponding frame may further include HEW-SIG Length Extend (HLE)information indicating the length information.

When a terminal having data to be transmitted receives a non-legacywireless LAN signal (i.e., a non-legacy wireless LAN signal of otherBSS) having BSS identifier information different from that of thecorresponding terminal, the terminal may perform channel access based ona CCA procedure according to the above-mentioned embodiment. In thiscase, according to an embodiment of the present invention, the terminaluses at least one of LEN-1, LEN-2 and LEN-3 of the received non-legacywireless LAN signal of other BSS to adjust a data transmission period ofthe corresponding terminal. If the terminal transmits a single frame,the data transmission period may represent the duration of thecorresponding frame. If the terminal continuously transmits a pluralityof frames, the data transmission period may represent a transmissionopportunity (TXOP) of the corresponding terminal. A specific embodimentof this will be described with reference to FIGS. 21 to 23.

First, FIG. 21 illustrates an embodiment in which the data transmissionperiod of a terminal is adjusted based on the length information of areceived wireless LAN signal. Referring to FIG. 21, the terminal OT ofthe OBSS transmits data O_DATA to the terminal OR, and the terminal ORtransmits a response message O_ACK to the terminal OT in response to thereceived data O_DATA. When the terminal MT transmits the data MY_DATAwhile the data O_DATA is transmitted, the terminal MT extracts thelength information LEN(O_DATA) from the received wireless signal O_DATAand adjusts the transmission period of the data MY_DATA based on theextracted length information LEN(O_DATA). In this case, the extractedlength information LEN(O_DATA) includes at least one of LEN-1, LEN-2 andLEN-3 extracted from O_DATA. In the embodiment of FIG. 21, LEN-1 mayrepresent length information of O_DATA, and LEN-2 may represent totaltransmission length information of O_DATA+SIFS+O_ACK.

According to the embodiment of FIG. 21, the terminal MT adjusts thetransmission period of the MY_DATA being transmitted by thecorresponding terminal to be terminated simultaneously or before thetransmission completion time point of the wireless signal O_DATA, basedon the length information LEN(O_DATA) extracted from the wireless signalO_DATA. That is, the terminal MT adjusts the length of MY_DATA beingtransmitted by the corresponding terminal to be LEN(O_DATA) or less. Thewireless LAN data MY_DATA of the terminal MT may be transmitted in theform of a PLCP Protocol Data Unit (PPDU), and the terminal MT may adjustthe length of the wireless LAN data MY_DATA through various methods. Forexample, if the PPDU is composed of a single MAC Protocol Data Unit(MPDU), the terminal MT may perform fragmentation on the correspondingMPDU based on the extracted length information to reduce the length ofMY_DATA. In addition, if the PPDU is composed of aggregate MPDU(A-MPDU), the terminal MT may limit the number of MPDUs included in theA-MPDU, or may perform fragment on an individual MPDU based on theextracted length information to reduce the length of MY_DATA. Accordingto an embodiment, the terminal MT may refer to LLE information and/orHLE information of O_DATA when adjusting the length of MY_DATA.

On the other hand, in the embodiment of FIG. 21, when the transmissionperiod of MY_DATA ends at the same time as the transmission completiontime point of O_DATA, the response message MY_ACK of the terminal MR andthe response message O_ACK of the terminal OR are simultaneouslytransmitted. However, when MY_ACK and O_ACK are simultaneously receivedby the legacy terminal L, the legacy terminal L recognizes that acollision 830 between data occurs. Therefore, after the transmission ofthe response messages MY_ACK and O_ACK is terminated, the legacyterminal L may have a problem of accessing the channel after extendedinter frame spacing (EIFS) longer than AIFS.

Next, FIG. 22 illustrates another embodiment in which the datatransmission period of a terminal is adjusted based on the lengthinformation of a received wireless LAN signal. In the embodiment of FIG.22, duplicative description of parts, which are the same as orcorrespond to the embodiment of FIG. 21, will be omitted.

According to the embodiment of FIG. 22, the terminal MT adjusts thetransmission period of MY_DATA being transmitted by the correspondingterminal to be terminated before the transmission completion time pointof the wireless signal O_DATA, based on the length informationLEN(O_DATA) extracted from the wireless signal O_DATA. That is, theterminal MT adjusts the length of MY_DATA being transmitted by thecorresponding terminal to be less than LEN(O_DATA). More specifically,referring to FIG. 22, the terminal MT sets the length of MY_DATA toLEN(O_DATA)—LEN(MY_ACK)—SIFS or less. Here, LEN(MY_ACK) represents thelength of MY_ACK. That is, the terminal MT sets the transmission periodof MY_DATA to be terminated earlier than the transmission completiontime point of O_DATA by the sum of a SIFS time and a time required forthe transmission of the response message MY_ACK. Therefore, in theembodiment of FIG. 22, the transmission of MY_DATA and the correspondingMY_ACK ends within the transmission period of O_DATA.

On the other hand, the terminal MT, the terminal MR, or other terminalsin the MYBSS may attempt to transmit data while O_ACK is transmitted.According to an embodiment, arbitrary information may be inserted intopredetermined specific messages such as request-to-send (RTS),clear-to-send (CTS), and ACK messages. In this case, when a messageincluding the corresponding information is received, the adjustment of aCCA threshold according to the above-described embodiment may not beallowed. That is, terminals of other BSS receiving the message performchannel access based on the first CCA threshold CCA-SD 1 rather than thesecond CCA threshold CCA-SD 2.

In such a manner, according to the embodiment of FIG. 22, all terminalsincluding the legacy terminal attempt channel access when the channel isin an idle state for an AIFS time after the O_ACK transmission of theterminal OR is completed. Therefore, a fair opportunity of channelaccesses between the non-legacy terminal and the legacy terminal may beguaranteed.

FIG. 23 illustrates another embodiment in which the data transmissionperiod of a terminal is adjusted based on the length information of areceived wireless LAN signal. In the embodiment of FIG. 23, duplicativedescription of parts, which are the same as or correspond to theembodiments of FIGS. 21 and 22, will be omitted.

According to the embodiment of FIG. 23, the terminal OT of the OBSScontinuously transmits a plurality of data O_DATA-1, O_DATA-2, andO_DATA-3 during the TXOP period OT_TXOP allocated to the correspondingterminal. In the case of a Quality of Service (QoS) terminal thattransmits video data, voice data, and the like, a plurality of dataincluding at least one subsequence frame may be continuously transmittedduring a TXOP period allocated to the corresponding terminal. Inaddition, the terminal OR receiving a plurality of data from theterminal OT transmits response messages O_ACK-1, O_ACK-2, and O_ACK-3corresponding to each received frame. The transmission of a plurality ofdata and response messages corresponding thereto is completed within theTXOP period OT_TXOP allocated to the terminal OT.

When the terminal MT transmits data while the terminal OT transmits aplurality of data, the terminal MT extracts length information from atleast one of the plurality of data O_DATA-1, O_DATA-2 and O_DATA-3, andadjusts the data transmission period of the corresponding terminal basedon the extracted length information. In this case, the terminal MT mayextract the length information from the received data of the terminal OTin the process of performing CCA for data transmission of thecorresponding terminal. If the terminal MT transmits single data, thedata transmission period may mean duration of the corresponding dataframe. If the terminal MT continuously transmits a plurality of data,the data transmission period may mean a transmission opportunity (TXOP)of the corresponding terminal.

When the terminal MT transmits data during the transmission of O_DATA-1as in the embodiment of FIG. 23, the terminal MT extracts lengthinformation LEN(O_DATA-1) from O_DATA-1 and adjusts the datatransmission period of the corresponding terminal MT based on theextracted length information LEN(O_DATA-1). In this case, the extractedlength information LEN(O_DATA-1) includes at least one of LEN-1, LEN-2and LEN-3 extracted from O_DATA-1. In the embodiment of FIG. 23, LEN-1may represent the length of data O_DATA-1 where corresponding lengthinformation is extracted, LEN-2 may represents the length of a TXOPperiod OT_TXOP, that is,(O_DATA-1+SIFS+O_ACK-1)+SIFS+(O_DATA-2+SIFS+O_ACK-2)+SIFS+ . . .SIFS+(O_DATA-n+SIFS+O_ACK-n), which is allocated to the terminal OT thattransmits the corresponding data O_DATA-1. Additionally, LEN-3represents an arbitrary length defined by MAC.

As described above, the information represented by LEN-1 and LEN-2 isnot limited thereto and may be modified through other methods. Forexample, LEN-1 may represent the length of the TXOP period OT_TXOPallocated to the terminal OT that transmits the corresponding dataO_DATA-1. If LEN-1 represents length information (for example, totaltransmission length information) exceeding the length of thecorresponding data O_DATA-1, O_DATA-1 may further include L-SIG LengthExtend (LLE) information indicating this. In the same manger, If LEN-2represents length information (for example, total transmission lengthinformation) exceeding the length of the corresponding data O_DATA-1,O_DATA-1 may further include HEW-SIG Length Extend (HLE) informationindicating this.

According to the embodiment of FIG. 23, the terminal MT adjusts the datatransmission period of the terminal MT to be terminated before the datatransmission completion time point of the terminal OT, based on theextracted length information LEN(O_DATA-1). When a terminal continuouslytransmits a plurality of data as in the embodiment of FIG. 23, thelength of the TXOP period MT_TXOP allocated to the terminal MT, that is,(MY_DATA-1+SIFS+MY_ACK-1)+SIFS+(MY_DATA-2+SIFS+MY_ACK-2)+SIFS+ . . .+SIFS+(MY_DATA-m+SIFS+MY_ACK-m), may be set shorter than the length ofthe TXOP period OT_TXOP allocated to the terminal OT. More specifically,referring to FIG. 23, the length of the TXOP period MT_TXOP allocated tothe terminal MT may be set to OT_TXOP—LEN(O_ACK)—SIFS or less. That is,the terminal MT adjusts the total sum of the lengths of one or aplurality of data transmitted by the corresponding terminal to be equalto or smaller than LEN-2(O_DATA-1)—LEN(O_ACK-n)—LEN(MY_ACK-m)—SIFS.Here, it is assumed that OT_TXOP information is extracted from LEN-2 ofO_DATA-1, and LEN-2(O_DATA-1) represents the extracted LEN-2information. Also, LEN(O_ACK-n) represents the length of a responsemessage to the last transmission data O_DATA-n of the terminal OT, andLEN(MY_ACK-m) represents the length of a response message to the lasttransmission data (MY_DATA-m) of the terminal MT.

Accordingly, in the embodiment of FIG. 23, the transmission of one or aplurality of data MY_DATA-1 and MY_DATA-2 transmitted by the terminal MTand response messages MY_ACK-1 and MY_ACK-2 corresponding thereto iscompleted within the TXOP period OT_TXOP allocated to the terminal OT.All terminals including the legacy terminals attempt to access thechannel when the channel is in an idle state for an AIFS time after thetransmission of the last response message O_ACK-n of the terminal OR iscompleted. Therefore, a fair opportunity of channel accesses between thenon-legacy terminal and the legacy terminal may be guaranteed.

As described above, according to an embodiment of the present invention,the terminal MT may determine the data transmission period of thecorresponding terminal by using the length information LEN-1 or LEN-2extracted from the L-SIG field or the HEW-SIG field of the receivedwireless signal O_DATA. In this case, the terminal MT may adjust thedata transmission period of the corresponding terminal in a short timebefore decoding the MAC header of the O_DATA.

FIG. 24 illustrates another embodiment of the present invention to solvethe unfairness problem of a legacy terminal that may occur if anadjusted CCA threshold is used for channel access. In the embodiment ofFIG. 24, HE, HE0, HE1, HE2, HE3, HE A, and HE B represent non-legacyterminals, respectively, and Leg and Leg X represent legacy terminals.In addition, terminals HE1, HE2, HE3, and Leg X are associated with afirst BSS operated by HE A, and terminal HE, HE0, and Leg are associatedwith a second BSS operated by HE B.

In the embodiment of FIG. 24, when the terminal HE0 of the second BSStransmits data, the signal of the corresponding data may be detected bythe terminals of the adjacent first BSS. When the wireless signal ofother BSS is detected in such a way, the non-legacy terminals HE1, HE2,and HE3 of the first BSS perform CCA based on the second CCA thresholdCCA-SD 2 described above, and the legacy terminal Leg X performs CCAbased on the first CCA threshold CCA-SD 1. When it is assumed that thedata of the terminal HE0 is received by the respective terminals as thereceived signal strength between the first CCA threshold CCA-SD1 and thesecond CCA threshold CCA-SD2, the non-legacy terminals HE1, HE2, and HE3may perform backoff procedures by reducing backoff counters backoff 1,backoff 2, and backoff 3 assigned to the corresponding terminals.However, the legacy terminal Leg X may not perform a backoff procedureand defer the channel access, resulting in unfairness problem.

In addition, when the data transmission of the terminals HE0 and HE1 iscompleted and the channel becomes in an idle state, the non-legacyterminals HE2 and HE3 respectively resume backoff procedures by usingthe remaining backoff counters, for example, the remaining backoff 2 andthe remaining backoff 3 from previous backoff procedures. However, sincethe legacy terminal Leg X filed to reduce the backoff counter during theprevious backoff procedure of the non-legacy terminals, it resumes thebackoff procedure by using the backoff counter backoff X previouslyassigned to the corresponding terminal. Therefore, the legacy terminalhas less probability of accessing the channel than the non-legacyterminal even in the subsequent contention window interval.

In order to solve such a problem, according to an embodiment of thepresent invention, by adjusting a backoff counter used in a backoffprocedure of non-legacy terminals in a spatial reuse period, thefairness of channel accesses between the non-legacy terminals and thelegacy terminals may be maintained. In the present invention, thespatial reuse period refers to a period in which channel access isperformed based on an adjusted CCA threshold when the BSS identifierinformation of a received wireless signal is different from the BSSidentifier information of a terminal.

In the spatial reuse period, the non-legacy terminals HE1, HE2, and HE3of the first BSS perform CCA based on the second CCA threshold CCA-SD 2.If it is determined that the corresponding channel is in an idle stateas a result of the CCA, the non-legacy terminals perform backoffprocedures by using backoff counters assigned to each terminal. In theembodiment of FIG. 24, the terminal HE1 whose backoff counter expiresfirst transmits data during the performing of the backoff procedures. Inthis case, the backoff procedures of the remaining terminals HE2 and HE3are suspended.

If such a backoff procedure is suspended, the non-legacy terminal mayadjust the backoff counter assigned to the corresponding terminal. Thenon-legacy terminal may resume the backoff procedure by using theadjusted backoff counter when the corresponding channel becomes in anidle state again. According to an embodiment, the non-legacy terminalmay restore the backoff counter that is reduced during the backoffprocedure in the spatial reuse period to a value before the backoffprocedure. According to another embodiment, the non-legacy terminal maybe assigned a new backoff counter if the backoff procedure is suspendedin the spatial reuse period. Such an adjustment of the backoff countermay be performed when the received signal strength of a wireless signalhaving BSS identifier information different from that of thecorresponding terminal is between the first CCA threshold CCA-SD 1 andthe second CCA threshold CCA-SD 2.

On the other hand, according to another embodiment of the presentinvention, the non-legacy terminal may perform channel access by using aplurality of backoff counters. For example, the non-legacy terminal maybe assigned a first backoff counter and a second backoff counter for thebackoff procedure. In this case, the non-legacy terminal performs thebackoff procedure by using at least one of the first backoff counter andthe second backoff counter based on the received signal strength of thereceived wireless signal. For example, the non-legacy terminal mayconsume the first backoff counter when the received signal strength of awireless signal having BSS identifier information different from that ofthe corresponding terminal is lower than the first CCA threshold CCA-SD1. And the non-legacy terminal may consume the second backoff counterwhen the received signal strength of the wireless signal is between thefirst CCA threshold CCA-SD 1 and the second CCA threshold CCA-SD 2. Thenon-legacy terminal may transmit data when at least one of the firstbackoff counter and the second backoff counter expires.

In such a manner, the non-legacy terminal according to the embodiment ofFIG. 24 adjusts the backoff counter used for the backoff procedure orperforms the backoff procedure by using a plurality of backoff countersin the spatial reuse period, to minimize an unfairness that may occur inthe legacy terminal.

FIG. 25 is a diagram illustrating an interference problem that may occurif an adjusted CCA threshold is used for channel access according to anembodiment of the present invention. According to the embodiment of FIG.25 and the following embodiments, a MYBSS Transmitter (MT) and a MYBSSReceiver (MR) represents a transmission terminal and a receptionterminal of a first BSS, respectively, and an OBSS Transmitter (OT) andan OBSS Receiver (OR) represent a transmission terminal and a receptionterminal of a second BSS different from the first BSS.

As shown in FIG. 25, in the OBSS, the terminal OT may transmit dataO_DATA to the terminal OT and the terminal OR may transmit a responsemessage O_ACK to the terminal OT in response to the received dataO_DATA. On the other hand, the terminal MT of the MYBSS different fromthe OBSS determines whether the channel is busy based on the receivedsignal strength of the wireless signal O_DATA and the BSS identifierinformation of the corresponding signal, as in the above embodiment.That is, if the BSS identifier information of the received wirelesssignal O_DATA is different from the BSS identifier information of thecorresponding terminal, the terminal MT performs CCA based on the secondCCA threshold CCA-SD 2. In this case, the second CCA threshold CCA-SD 2has a higher level than the first CCA threshold CCA-SD 1 used in thelegacy terminal.

If the received signal strength of O_DATA is lower than the second CCAthreshold CCA-SD 2, the terminal MT determines that the channel is in anidle state and performs channel access. That is, the terminal MTperforms a backoff procedure and transmits data MY_DATA when the backoffcounter of the backoff procedure expires. In addition, the terminal MRreceiving MY_DATA from the terminal MT transmits a response messageMY_ACK in response thereto.

However, since the channel access of the terminal MT is determined basedon the received signal strength of O_DATA transmitted by the terminalOT, MY_DATA transmitted by the terminal MT may cause interference to theterminal OR of the OBSS. Such a problem may occur not only in a singleMAC Protocol Data Unit (MPDU) transmission but also in transmissionsituations based on transmission opportunity (TXOP) or aggregate MPDU(A-MPDU).

FIGS. 26 to 27 are diagrams illustrating the data transmission method ofa non-legacy terminal for minimizing an interference problem betweenterminals. In the embodiments of FIGS. 26 and 27, the terminal OT of theOBSS may transmit one or a plurality of data O_DATA-1 and O_DATA-2 tothe terminal OR and the data is referred to as O_DATA. Additionally, theterminal MT of the MYBSS may transmit one or a plurality of dataMY_DATA-1 and MY_DATA-2 to the terminal MR, and the data is referred toas MY_DATA.

First, FIG. 26 is a diagram illustrating an embodiment for minimizingthe interference that the terminal MT affects the terminal OR in theOBSS. Referring to FIG. 26, terminals performing wireless LANcommunication may exchange a request (REQ) message and a response (RSP)message before data transmission. In an embodiment of the presentinvention, the request message/response message may representrequest-to-send (RTS)/clear-to-send (CTS), a null data packet (NDP)/ACK,or a single MAC Protocol Data Unit (MPDU)/ACK, respectively. In theembodiment of FIG. 26, it is assumed that a request message O_REQtransmitted by the terminal OT of the OBSS and a response message O_RSPtransmitted by the terminal OR may be received by the terminal MT of theMYBSS.

According to an embodiment of the present invention, when the terminalMT of the MYBSS receives the request message O_REQ having different BSSidentifier information from that of the corresponding terminal and aresponse message O_RSP corresponding thereto, the terminal MT maydetermine whether to access a channel, that is, whether to transmit dataMY_DATA of the corresponding terminal based on the received signalstrengths of O_REQ and O_RSP. In this case, the terminal MT determineswhether to transmit MY_DATA based on the result of comparing thereceived signal strengths of O_REQ and O_RSP with the first CCAthreshold CCA-SD 1 and the second CCA threshold CCA-SD 2. Herein, thesecond CCA threshold CCA-SD 2 has a higher level than the first CCAthreshold CCA-SD 1.

First, if the received signal strength of at least one of O_REQ andO_RSP is higher than the second CCA threshold CCA-SD 2, the terminal MTdefers the transmission of MY_DATA. Additionally, even when the receivedsignal strengths of O_REQ and O_RSP are both between the first CCAthreshold CCA-SD 1 and the second CCA threshold CCA-SD 2, the terminalMT defers the transmission of MY_DATA. However, in this case, theterminal MT may exceptionally perform data transmission according toother additional information such as the importance of data to betransmitted. On the other hand, if the received signal strengths ofO_REQ and O_RSP are both lower than the first CCA threshold CCA-SD 1,the terminal MT may access the channel and perform the transmission ofMY_DATA.

Next, if the received signal strength of O_REQ is between the first CCAthreshold CCA-SD 1 and the second CCA threshold CCA-SD 2, and thereceived signal strength of O_RSP is lower than the first CCA thresholdCCA-SD 1, the terminal MT may access the channel and perform thetransmission of MY_DATA. Therefore, if the received signal strength ofO_RSP is lower than the first CCA threshold CCA-SD 1 in a situationwhere the received signal strength of O_REQ is lower than the second CCAthreshold CCA-SD 2, the terminal MT may access the channel and performthe transmission of MY_DATA. In this case, it is assumed that theinfluence of the interference to the terminal OR by the MY_DATAtransmitted by the terminal MT is small. Therefore, the terminal OR maysuccessfully receive the data O_DATA-1 and O_DATA-2 transmitted by theterminal OT. In such a way, a period in which channel access isperformed based on an adjusted CCA threshold when the BSS identifierinformation of a received wireless signal is different from the BSSidentifier information of a terminal is referred to as a spatial reuseperiod.

According to an embodiment of the present invention, the terminal MTtransmitting data in the spatial reuse period may transmit dataimmediately without exchanging a separate request message and responsemessage. In addition, the terminal MT may continuously measure thereceived signal strength of data transmitted by the OBSS terminals inthe spatial reuse period, and adjust whether to access the channel inreal time based on the measured result. In this case, the same criterionas O_REQ is applied to the data O_DATA-1 and O_DATA-2 transmitted by theterminal OT of the OBSS, and the same criterion as O_RSP may be appliedto the data O_ACK-1 and O_ACK-2 transmitted by the terminal OR. If thereceived signal strength of the data transmitted by the OBSS terminalsbelongs to a signal strength section equal to the received signalstrength of O_REQ or O_RSP corresponding thereto, the terminal MTmaintains the operation based on the predetermined channelaccessibility. However, if the received signal strength of the datatransmitted by the OBSS terminals belongs to a signal strength sectiondifferent from the received signal strength of O_REQ or O_RSPcorresponding thereto, the terminal MT redetermines whether to accessthe channel based on the received signal strength of the received data.Here, the received signal strength section includes a first sectionlower than the first CCA threshold CCA-SD 1, a second section betweenthe first CCA threshold CCA-SD 1 and the second CCA threshold CCA-SD 2,and a third section greater than the second CCA threshold CCA-SD 2.

If O_REQ and O_RSP include the length information according to theabove-described embodiment, the terminal MT receiving O_REQ and O_RSPmay extract the length information from the corresponding message andadjust the data transmission period of the corresponding terminal MTbased on the extracted length information. In this case, the terminal MTmay omit the operation of extracting the length information from thedata O_DATA-1 and O_DATA-2 transmitted by the terminal OT.

Next, FIG. 27 is a diagram illustrating a further embodiment forminimizing the interference to the terminal MR of the MYBSS. In theembodiment of FIG. 27, duplicative description of parts, which are thesame as or correspond to the embodiment of FIG. 26, will be omitted.

As described above in the embodiment of FIG. 26, when the terminals ofthe OBSS transmit O_REQ and O_RSP, the terminals MT and MR of the MYBSSmay receive the O_REQ and O_RSP. The terminal MT of the MYBSS determineswhether to access the channel based on the received signal strength ofO_REQ and O_RSP. According to the embodiment of FIG. 27, when it isdetermined that the terminal MT accesses the channel, the terminal MTtransmits a request message MY_REQ to the terminal MR. MY_REQ is amessage indicating that the data transmission of the terminal MT ispossible and may be implemented by request-to-send (RTS), null datapacket (NDP), or single MAC Protocol Data Unit (MPDU).

The terminal MR receiving MY_REQ from the terminal MT determines whetherto receive the data MY_DATA of the terminal MT based on the receivedsignal strengths of O_REQ and O_RSP. In this case, the terminal MRdetermines whether MY_DATA can be received based on the result ofcomparing the received signal strengths of O_REQ and O_RSP with thefirst CCA threshold CCA-SD 1 and the second CCA threshold CCA-SD 2.Herein, the second CCA threshold CCA-SD 2 has a higher level than thefirst CCA threshold CCA-SD 1.

First, if the received signal strength of at least one of O_REQ andO_RSP is higher than the second CCA threshold CCA-SD 2, the terminal MRmay not receive MY_DATA. Additionally, even when the received signalstrengths of O_REQ and O_RSP are both between the first CCA thresholdCCA-SD 1 and the second CCA threshold CCA-SD 2, the terminal MR may notreceive MY_DATA. However, in this case, the terminal MR mayexceptionally receive data according to other additional informationsuch as the importance of MY_DATA. On the other hand, if the receivedsignal strengths of O_REQ and O_RSP are both lower than the first CCAthreshold CCA-SD 1, the terminal MR may receive MY_DATA.

Next, if the received signal strength of O_RSP is between the first CCAthreshold CCA-SD 1 and the second CCA threshold CCA-SD 2, and thereceived signal strength of O_REQ is lower than the first CCA thresholdCCA-SD 1, the terminal MR may receive MY_DATA. Therefore, if thereceived signal strength of O_REQ is lower than the first CCA thresholdCCA-SD 1 in a situation where the received signal strength of O_RSP islower than the second CCA threshold CCA-SD 2, the terminal MR mayreceive MY_DATA. In this case, it is assumed that the influence of theinterference to the terminal MR by O_DATA transmitted by the terminal OTis small. Therefore, the terminal MR may successfully receive the dataMY_DATA-1 and MY_DATA-2 transmitted by the terminal MT.

The terminal MR transmits a response message MY_RSP corresponding toMY_REQ transmitted by the terminal MT, based on whether or not MY_DATAcan be received. MY_RSP is a message indicating that data of theterminal MT can be received, and may be implemented by clear-to-send(CTS) or ACK. If the terminal MR is able to receive MY_DATA, theterminal MR transmits MY_RSP corresponding to MY_REQ to the terminal MT.When MY_RSP is received from the terminal MR, the terminal MT may startthe transmission of MY_DATA. However, if the terminal MR is not able toreceive MY_DATA, the terminal MR does not transmit MY_RSP. When MY_RSPis not received from the terminal MR, the terminal MT may not transmitMY_DATA. In such a way, according to the embodiment of FIG. 27, theterminals of the MYBSS exchange MY_REQ and MY_RSP in the spatial reuseperiod, so that it is possible to additionally determine whether or notthe terminal MR is able to receive the data MY_DATA of the terminal MTwithout interference.

FIGS. 28 and 29 are diagrams illustrating another interference problemthat may occur if an adjusted CCA threshold is used for channel accessaccording to an embodiment of the present invention. In the embodimentsof FIGS. 28 and 29, duplicative description of parts, which are the sameas or correspond to the embodiment of FIG. 25, will be omitted.

As shown in FIGS. 28 and 29, in the OBSS, the terminal OT may transmitdata O_DATA to the terminal OR and the terminal OR may transmit aresponse message O_ACK to the terminal OT in response to the receiveddata O_DATA. On the other hand, the terminal MT of the MYBSS, which is aBSS different from the OBSS, determines whether or not the channel isbusy according to the above-described embodiment, and performs channelaccess. That is, the terminal MT performs a backoff procedure andtransmits data MY_DATA when the backoff counter of the backoff procedureexpires. In addition, the terminal MR receiving MY_DATA from theterminal MT transmits a response message MY_ACK in response thereto.

However, MY_ACK transmitted by the terminal MR may cause interference tothe terminals of the OBSS. Referring to FIG. 28, MY_ACK transmitted bythe terminal MR may cause interference when the terminal OR receives thedata O_DATA of the terminal OT. In addition, referring to FIG. 29,MY_ACK transmitted by the terminal MR may cause interference when theterminal OT receives the response message O_ACK of the terminal OR.

FIG. 30 is a diagram illustrating the data transmission method of anon-legacy terminal for minimizing an interference problem betweenterminals according to another embodiment of the present invention. Inthe embodiment of FIG. 30, duplicative description of parts, which arethe same as or correspond to the embodiments of FIGS. 26 and 27, will beomitted.

As shown in the drawing, when the terminals of the OBSS transmit O_REQand O_RSP, the terminals MT and MR of the MYBSS may receive O_REQ andO_RSP. As in the above-described embodiment, the terminal MT of theMYBSS determines whether to access the channel based on the receivedsignal strengths of O_REQ and O_RSP, and transmits the data MY_DATA. Inaddition, the terminal MR receiving MY_DATA transmits a response messageMY_ACK in response thereto. According to an embodiment of the presentinvention, the terminal MR may determine the transmission time point ofMY_ACK based on the received signal strengths of O_REQ and O_RSP. Inthis case, the terminal MR determines the transmission time point ofMY_ACK based on the result of comparing the received signal strengths ofO_REQ and O_RSP with the first CCA threshold CCA-SD 1 and the second CCAthreshold CCA-SD 2. Herein, the second CCA threshold CCA-SD 2 has ahigher level than the first CCA threshold CCA-SD 1.

First, if the received signal strength of O_REQ is between the first CCAthreshold CCA-SD 1 and the second CCA threshold CCA-SD 2, and thereceived signal strength of O_RSP is lower than the first CCA thresholdCCA-SD 1, the terminal MR transmits MY_ACK 841 within the transmissionperiod of the data O_DATA of the terminal OT. In this case, it isassumed that the influence of the interference to the terminal OR of theOBSS by MY_ACK 841 transmitted by the terminal MR is small. Therefore,the terminal OR may successfully receive O_DATA transmitted by theterminal OT.

Next, if the received signal strength of O_RSP is between the first CCAthreshold CCA-SD 1 and the second CCA threshold CCA-SD 2, and thereceived signal strength of O_REQ is lower than the first CCA thresholdCCA-SD 1, the terminal MR transmits MY_ACK 842 simultaneously when theterminal OR transmits the response message O_ACK. In this case, it isassumed that the influence of the interference to the terminal OT of theOBSS by MY_ACK 842 transmitted by the terminal MR is small. Accordingly,the terminal OT may successfully receive O_ACK transmitted by theterminal OR.

Next, if the received signal strengths of O_REQ and O_RSP are bothhigher than the second CCA threshold CCA-SD 2, the terminal MR transmitsMY_ACK 843 after the transmissions of the data O_DATA of the terminal OTand the response message O_ACK of the terminal OR are completed. In thiscase, it is assumed that MY_ACK 843 transmitted by the terminal MRinterferes with the terminals OT and OR of the OBSS. Therefore, sincethe terminal MR transmits MY_ACK 843 after the data exchange of theterminals OT and OR is completed, so that data collision that may occurto the OBSS terminals may be prevented.

According to a further embodiment of the present invention, the terminalMR may adjust the transmission power of MY_ACK in consideration of thetransmission power of the corresponding terminal and the received signalstrength of MY_DATA. Through this, the terminal MR may minimize theamount of interference that MY_ACK gives to the terminal OT or theterminal OR.

Although the present invention is described by using the wireless LANcommunication as an example, the present invention is not limitedthereto and the present invention may be similarly applied even to othercommunication systems such as cellular communication, and the like.Further, the method, the apparatus, and the system of the presentinvention are described in association with the specific embodiments,but some or all of the components and operations of the presentinvention may be implemented by using a computer system having universalhardware architecture.

The detailed described embodiments of the present invention may beimplemented by various means. For example, the embodiments of thepresent invention may be implemented by a hardware, a firmware, asoftware, or a combination thereof.

In case of the hardware implementation, the method according to theembodiments of the present invention may be implemented by one or moreof Application Specific Integrated Circuits (ASICSs), Digital SignalProcessors (DSPs), Digital Signal Processing Devices (DSPDs),Programmable Logic Devices (PLDs), Field Programmable Gate Arrays(FPGAs), processors, controllers, micro-controllers, micro-processors,and the like.

In case of the firmware implementation or the software implementation,the method according to the embodiments of the present invention may beimplemented by a module, a procedure, a function, or the like whichperforms the operations described above. Software codes may be stored ina memory and operated by a processor. The processor may be equipped withthe memory internally or externally and the memory may exchange datawith the processor by various publicly known means.

The description of the present invention is used for exemplification andthose skilled in the art will be able to understand that the presentinvention can be easily modified to other detailed forms withoutchanging the technical idea or an essential feature thereof. Thus, it isto be appreciated that the embodiments described above are intended tobe illustrative in every sense, and not restrictive. For example, eachcomponent described as a single type may be implemented to bedistributed and similarly, components described to be distributed mayalso be implemented in an associated form.

The scope of the present invention is represented by the claims to bedescribed below rather than the detailed description, and it is to beinterpreted that the meaning and scope of the claims and all the changesor modified forms derived from the equivalents thereof come within thescope of the present invention.

MODE FOR INVENTION

As above, related features have been described in the best mode.

INDUSTRIAL APPLICABILITY

Various exemplary embodiments of the present invention have beendescribed with reference to an IEEE 802.11 system, but the presentinvention is not limited thereto and the present invention can beapplied to various types of mobile communication apparatus, mobilecommunication system, and the like.

The invention claimed is:
 1. A wireless communication terminalcomprising: a transceiver configured to transmit and receive wirelesssignals; and a processor configured to process wireless signalstransmitted or received through the transceiver, wherein the processoris configured to: receive a first packet through the transceiver,measure a received signal strength of the first packet, determinewhether the first packet is a packet of a basic service set (BSS) withwhich the terminal is associated or a packet of a different BSS from theBSS with which the terminal is associated, and access a channel based onthe received signal strength of the first packet when the first packetis determined to be the packet of the different BSS from the BSS withwhich the terminal is associated.
 2. The terminal of claim 1, whereintransmission of a packet by the terminal is allowed when the receivedsignal strength of the first packet is below a set value.
 3. Theterminal of claim 2, wherein the transmission of a packet by theterminal is allowed within a transmission period of a second packettransmitted in response to the first packet.
 4. The terminal of claim 1,wherein whether to access the channel depends on whether an intendedtransmission power of a packet to be transmitted by the terminal isbelow a threshold determined based on the received signal strength ofthe first packet.
 5. The terminal of claim 4, wherein as the receivedsignal strength of the first packet is higher, an allowed transmissionpower of the packet to be transmitted by the terminal is lower.
 6. Theterminal of claim 1, wherein the processor is further configured to:extract BSS identifier information of the first packet, compare the BSSidentifier information of the first packet with BSS identifierinformation of the BSS with which the terminal is associated, anddetermine whether the first packet is the packet of the BSS with whichthe terminal is associated or the packet of the different BSS from theBSS with which the terminal is associated based on a result of comparingthe BSS identifier information.
 7. A wireless communication method of aterminal, the method comprising: receiving a first packet; measuring areceived signal strength of the first packet; determining whether thefirst packet is a packet of a basic service set (BSS) with which theterminal is associated or a packet of a different BSS from the BSS withwhich the terminal is associated; and accessing a channel based on thereceived signal strength of the first packet when the first packet isdetermined to be the packet of the different BSS from the BSS with whichthe terminal is associated.
 8. The method of claim 7, whereintransmission of a packet by the terminal is allowed when the receivedsignal strength of the first packet is below a set value.
 9. The methodof claim 8, wherein the transmission of a packet by the terminal isallowed within a transmission period of a second packet transmitted inresponse to the first packet.
 10. The method of claim 7, wherein whetherto access the channel depends on whether an intended transmission powerof a packet to be transmitted by the terminal is below a thresholddetermined based on the received signal strength of the first packet.11. The method of claim 10, wherein as the received signal strength ofthe first packet is higher, an allowed transmission power of the packetto be transmitted by the terminal is lower.
 12. The method of claim 7,wherein the determining step further comprises: extracting BSSidentifier information of the first packet; comparing the BSS identifierinformation of the first packet with BSS identifier information of theBSS with which the terminal is associated; and determining whether thefirst packet is a packet of the BSS with which the terminal isassociated or the packet of the different BSS from the BSS with whichthe terminal is associated based on a result of comparing the BSSidentifier information.